British Gas has received over double the number of complaints than all other suppliers combined, according to industry watchdog energywatch.
The increase in complaints comes after the installation of a new billing system, although there are mixed reports as to whether the new system is the cause of customers' unhappiness.
Since the SAP-based system began implementation two years ago, it now covers all 17 million British Gas accounts, a spokeswoman said. Managing director Phil Bentley told media that the system had "teething problems", which were being sorted out.
"I understand what it's like to get a bill that's incorrect. We apologise to those customers and we're working very hard to improve services. We have put in a new system. It's working, but there are some teething problems," media reports quoted him as saying.
A British Gas spokeswoman said the problems had more to do with customer service than the new system, which she said was one of the biggest rollouts of SAP in Europe. "It is robust and working very well," she said of the billing system.
According to media reports, over-billing, incorrect metre readings, out-of-date account information and call centre delays have led over 14,000 customers to complain to energywatch in March alone.
Between October 2006 and this March, the watchdog received 21,427 complaints about the gas supplier, compared to 8,012 the year before.
"The events that led to chaotic customer services from British Gas could have happened to any company," said energywatch's director of campaigns Adam Scorer. "What consumers find unforgivable is the failure of British Gas to offer help and the high standards of customer service that consumers deserve. Their inability to deal with customers' problems is inexcusable - customers should not be left hanging on the phone or having to explain their circumstances to several different advisers."
Bentley told BBC Radio the problem should be fixed within a few months. "I'm on record as saying we will see significant improvements in service by summer."
