The transfers began on 16 November 2017, with $38m wired (then £32.3m) to a bank account in Dubai. A little later another sum, this time $15m, exited, followed by a third for $4m. At the start of the day, the bank account of Sonangol, Angola’s state oil company, had contained $57m. By sunset, it had just $309.

The story of these payments, as told by a Sonangol bank statement and internal report, lies at the centre of an Angolan government investigation into Africa’s richest woman.

Isabel dos Santos, 46, says the Angolan government is presenting a series of highly selective, or even fabricated, documents to attack her. “Today I’m facing charges that are completely false. These allegations have absolutely no grounds whatsoever, and they’re completely politically motivated,” she told BBC News.

Q&A What is the Luanda Leaks investigation? Show The Luanda Leaks project is based on a trove of 715,000 emails, charts, contracts, audits and accounts detailing the business operations of Isabel dos Santos, the daughter of the former president of Angola. The files were initially obtained by the anti-corruption charity Platform to Protect Whistleblowers in Africa (PPLAAF), which shared them with the International Consortium of Investigative Journalists (ICIJ). The documents, which cover a period between 1980 and 2018, have been reviewed by more than 120 journalists from 37 media outlets, including the Guardian, the BBC and the Portuguese newspaper Expresso.

The investigation relates to her management of Sonangol in 2016 and 2017, and events that took place in the days before her sacking.

As Africa’s second-largest oil producer Angola has vast petroleum wealth, which is licensed exclusively by Sonangol. It has ventures in a swath of other sectors, such as helicopters, telecoms and real estate, to support its core business. In 2018, its turnover was $18bn.

But by 2015 Sonangol was in crisis. The falling price of oil and longstanding inefficiency were draining the company’s revenues. With oil the keystone of the Angolan economy, responsible for a third of its GDP and 90% of its exports, a bankrupt Sonangol would mean economic catastrophe.

The government took drastic action. By decree of the then president, José Eduardo dos Santos, a committee to restructure the Angolan oil sector was constituted, and it invited a Maltese company, Wise Intelligence Solutions, to coordinate a group of consultants to advise on reforms . Wise’s owner was the president’s daughter, Isabel dos Santos.

She had no background in oil and gas, but believes she was selected for her extensive business experience. “They wanted to have a view of someone that’s coming in from the private sector, and to have private sector eyes look at a state enterprise,” she said.

Six months later, Isabel dos Santos would be granted even greater influence over the reforms. A second presidential decree announced her appointment as chair of Sonangol, mandated with overseeing its turnaround.

Dos Santos said her work on the first contract made her the logical choice for the commission. “Once we’d finished, they had difficulties recruiting a team that could actually go ahead and implement it, and I was invited to come in and head Sonangol,” she said.

Dos Santos says she spent the next year and a half dedicating herself to saving Sonangol. “We were working from nine in the morning until 10 at night,” she said. “During nine months of this time I was pregnant. My son was born on 31 July, and on 27 July I was in a board meeting. People were saying: ‘Shouldn’t you be going to the hospital?’”

But Angolan government documents describe a series of developments that are the focus of the investigation into Dos Santos by the Angolan government . They took place in the weeks before she was dismissed by her father’s successor, João Lourenço.

On 7 November 2017, the head of Sonangol’s London subsidiary was sacked, and the following day a company memo, signed by Dos Santos, announced that a woman called Maria Rodrigues would replace her. The memo was dated 30 August 2017.

Sonangol’s office in Brompton Place, London. Photograph: Martin Godwin/The Guardian

Within 48 hours, Rodrigues had signed a contract for consultancy services on behalf of the UK subsidiary, according to a Sonangol internal report. That contract’s counter-party was a Dubai company, Matter Business Solutions, and Matter’s signatory was a woman called Paula Oliveira. It was this contract, signed on 10 November by Oliveira and Rodrigues, that would be the basis on which millions of dollars were moved out of Sonangol’s bank account six days later, according to the company’s inquiry.

This month, Rodrigues told an International Consortium of Investigative Journalists (ICIJ) reporter she only recalled signing one document, because she was told to, before a Sonangol lawyer told her she had no authority to act for the company. She claimed she did not know what she was signing and had not heard of Oliveira.

Dos Santos’s lawyers said the decision to replace the head of the London subsidiary had been made on 30 August 2017, but “the public announcement of the appointment was deferred”. They said it was “simply incorrect” that Rodrigues did not have authority to sign documents.

Oliveira is a Portuguese human resources specialist and partner at a consulting firm. She also appears to be a close friend of Isabel dos Santos. The two can be seen together in Instagram posts, smiling with shared friends, and co-own a call centre business and a restaurant in Angola’s capital, Luanda.

Documents from Dubai, obtained by the ICIJ, name Matter’s shareholder as Oliveira. Mário da Silva, who manages Dos Santos’s companies and whose assets were also frozen in December, is named as a director.

Oliveira said she was, and had always been, the sole owner of Matter. Her lawyers said Matter was engaged by Sonangol, with the approval of the Angolan government, to lead and coordinate the plans to restructure Sonangol.

Her lawyers said her involvement in the project had been confidential for commercial reasons, and that although she knew Dos Santos the notion she was acting as her proxy was “simply fanciful”.

Da Silva did not respond to repeated requests for comment, though Oliveira said she hired him for his experience running Dos Santos’s company Wise.

Dos Santos denied the transfers were intended to empty Sonangol’s bank account before she was forced from office and said it was ludicrous to suggest she would even know the date of her own sacking in advance. “I did not know that I would be dismissed on the 16th, or whatever date of November it was,” she told the BBC. “I’m not clairvoyant.”

She said the contract with Matter was an extension of the arrangement established with her company Wise, coordinating consultancy firms as subcontractors, and was approved by the Sonangol board.

Her lawyers said that between June and November 2017 multiple invoices were paid, including those from November, to settle an unpaid bill for the consultants’ work.

“In order to settle the outstanding invoices, a number of payments began to occur between June and November 2017, with the final payment occurring by 15 November 2017,” they said, adding that the payments were for services delivered under contract.

The consultancy firms hired via Matter have distanced themselves from Dos Santos. PwC said it had terminated all ongoing work with her, while another, McKinsey, said it could not work with her until her legal position was clarified. BCG declined to comment on its restructure advice, though it is understood it considered its client to be the Angolan government rather than Dos Santos.

Dos Santos has denied all wrongdoing and is confident all allegations against her, including those surrounding Sonangol, will be proven false. But it is the suggestion that her success is down to her father’s influence that rankles the most.

“To try a person by the virtue of family, of a family bond, that doesn’t fly,” she told the BBC. “One has to be judged by one’s own work, one’s own merits.”