Telstra's budget mobile and internet provider Belong has overcharged customers overnight, debiting bank accounts multiple times.

Key points: Customers have been left unable to pay rent and buy necessities after Belong overcharged their accounts

Customers have been left unable to pay rent and buy necessities after Belong overcharged their accounts They say the company's phone line seemed to be down and its online chat system was not working

They say the company's phone line seemed to be down and its online chat system was not working Belong has emailed customers and said they were working on the issue

Customers have taken to the company's Facebook page to vent their frustrations.

"Not happy Belong," one customer posted.

"You've charged my account twice and have taken a portion of my rent money, that is due to be paid today as well. Please put the money back into my account so I can pay my landlord," wrote another.

"I have a 2 year old and a newborn that can't get formula or nappies for now because my account is in minus … I had $180 in my account and belong takes out 3 payments of $65 and I won't see that back usable in my account for 7-10 days."

Others are feeling the pinch close to Christmas.

"Christmas time isn't a great time financially for a lot of people and taking extra money and having to wait god knows how long for it to be returned is unacceptable," one woman posted.

Some customers have had triple payments taken out, with Belong then telling them their accounts with the company are now in credit.

Multiple payments were extracted from customers' bank accounts overnight. ( Facebook )

'Worst customer service ever'

Customers also expressed anger at the difficulty in getting hold of the company, saying its online chat system was not working and its phone line seemed to be down.

Many who did get through said they had been on hold for more than an hour.

"Worst customer service ever. On hold for over an hour to sort out you guys taking out my fee twice. Call sales and they answer instantly but are unable to help me. Obviously existing customers aren't important," posted one customer.

Belong has emailed customers addressing the reports.

"We are working on the issue right now and we'll refund the overpayment as soon as possible, " the email said.

In a statement Telstra said a system error had impacted its fixed broadband customers with Belong.

"We are currently contacting impacted customers and are working to refund any overpayments as quickly as possible," it said.

"We apologise for the inconvenience this has caused our customers."

It is not known how many of the company's 150,000 customers were affected.

"Having a company unexpectedly or unfairly take a direct debit from your account is a rude shock for any customer and can make a big impact," Choice spokesperson, Stefanie Menezes said.

"People could miss payments for other bills and face unnecessary financial stress in the lead up to Christmas.

"Big telco companies such as Telstra should have better systems in place to protect their customers from this kind of financial harm."