It was the bill that left Barbara Richards rubbing her eyes in disbelief.

In the three previous years, that quarter’s heating gas bill for the 105 apartments in one tower of her Sydney CBD unit complex had been $78, $208 and $97 respectively. But that year, in the second quarter of 2015, it was a stunning $10,377 – a rise over the year before of an astonishing 10,596 per cent.

“It was bewildering,” says Ms Richards, who looks after all the bills of the city centre apartment building Maestri Towers on Sussex and Kent streets. “I knew that couldn’t be right.

“There’d been nothing that had changed in our circumstances or our use of the gas heating for the apartments that could possibly explain such a phenomenal increase in our bill.”

It prompted members of the executive committee to take a much closer look at all their AGL gas bills, uncovering some increases of over 15,000 per cent. The building’s chair Michael Heaney was outraged. “This is the biggest scam in NSW since the bottom-of-the-harbour tax scams of the 1970s,” he says.

“The shocking thing is that this is going on because some buildings don’t know about checking their gas bills, and often they go straight to the strata manager to pay who may have no idea what’s going on. Many, as well, are on automatic payment.

The massive gas bill from AGL received by Michael Heaney and Barbara Richards. Photo: Ben Rushton

“One contractor we had in said he knows of 60 other buildings now all screaming about their gas bills. It’s a massive scam.”

Certainly, they’re not alone. In Zetland, Tony Zamora, the newly elected treasurer of another apartment building, was checking the previous three years’ financials and found that in 2013, the gas bill for his block was $2000. In 2014, that shot up to $150,000 and in 2015, $170,000 – an 85-fold rise in two years.

“It was absolutely outrageous!” he says. “I knew it couldn’t be right. If it had only gone up a little, we would have ignored it but going up by that much!”

Meanwhile, in nearby Kensington, the chair of a building in apartment complex Raleigh Park was also stupefied by their bills. “We’ve noticed a huge escalation in our bills,” says Norman Dusheiko.

The sudden bill increase prompted members of the executive committee to take a much closer look at all their AGL gas bills. Photo: Ben Rushton

“I think there’s a huge problem with them. We’ve been trying to get hold of our bills since May last year to check them, but it’s proving very difficult. We don’t know what’s happening. The last bill we even had a big credit, but we’re still trying hard to resolve the situation.”

The gas billing chaos has hit high-rise apartment buildings across Sydney, with all of them now being urged to check and re-check their bills to make sure they’re not being overcharged. The Energy & Water Ombudsman NSW has been called into at least one apartment building, but declined to return any of Fairfax Media’s calls.

AGL referred us to Jemena, the energy infrastructure company that owns the gas pipelines, physically distributes the gas and supplies the meter readings to the gas retailers, like AGL, for the bills.

A spokesman said, “Jemena acknowledges that billing issues can be worrying for our customers and apologises for any stress caused.

“Jemena confirms that the meter at [Maestri Towers] is read electronically by logging in remotely to a meter data logger. This meter has recently experienced a communications issue which has caused it to deliver faulty readings. We believe this may be caused by a third-party connection to the site.

“To resolve this issue Jemena is attending the site this week to conduct testing and repair work as required. Jemena hopes to have this issue resolved shortly, following which Jemena will work with AGL to revise and reissue customer bills.”

But Ms Richards says this follows months and months of complaining to AGL, with no result. All the meter readings labelled “actual” on their bills they found weren’t actual at all, as they differed wildly from what they could physically see – and what they photographed – on their meters.

At one point, AGL said it would only discuss the case in person at its Melbourne office. When the executive committee started making arrangements to fly to Melbourne, however, they were told a meeting wasn’t possible.

Mr Zamora had been passed from AGL onto Jemena. “But when I tried to speak to them, they said they don’t deal with the consumer, only the client which is AGL,” he says. “The whole process of questioning gas bills that are clearly wrong is extremely frustrating and I think they just rely on wearing you down.”

He, however, has finally triumphed. After his building paid $335,000 in gas bills over the past two years, he received a refund in December of a staggering $326,000.

“So we should have just been charged $9000 for those two years!” he says. “It’s astonishing, and nothing short of fraudulent. I still don’t know what went wrong; I was just so happy to get the money back.

“I think these companies rely on the fact that 99 per cent of their customers when they’re apartment buildings won’t bother to check or complain, and they’re really taking advantage of the consumer.”

Mr Heaney agrees. In his complex, the October-December period, a time when the heating was always switched off, leaving the maximum bill usually under $100 in service charges, the 2012 bill was $12,339.71. In 2013, it was even higher, at $13,465. And in 2014, $15,221 – an increase of more than 15,000 per cent.

“The difficulty is that apartment buildings operate on their own usually, so no one has any idea what is happening in others,” he says. “Luckily, we now have organisations like the Owners Corporation Network where we can get together and talk about such issues. But often unit blocks can be prime targets for getting ripped off.”