Sandra Wrench, 70, from Bedford, has fought a persistent battle with British Gas, making five complaints in a nine-month period. She says the utility giant made a string of errors, which mysteriously all seem to be weighted in its favour.Sandra was a customer with People’s Energy when it ceased trading on September 14, 2021, along with another 30 smaller suppliers at the time.She was automatically transferred to British Gas for both her gas and electricity, from October 11 last year.Then Sandra, from Bedford, realised that British Gas was charging her for energy in the weeks before she actually joined them.After she finally got through to the energy giant’s online chat service, British Gas agreed to refund £32.78 for gas and electricity plus standing charges of £10.51.It added up to £43.29 in total, as we reported in May.Sandra said while it may not sound a lot, but she lives alone and a family might secure a much larger refund.That was only the start of her one-woman campaign against charging injustice, and she fears many more British Gas customers have been caught out.’I always scrutinise my bills but others may not have the time and if paying by direct debit, just pay up without querying anything.’ Sandra Wrench feels British Gas could have done better (Image: Getty)Sandra also had credit of £73.34 with her previous energy company, People’s Energy, which had not been refunded to her.It was only transferred to her British Gas account on February 7, 2022.In July, she filed another complaint after British Gas started her new fixed-rate tariff on June 29, one day BEFORE her old tariff ended on June 30. ‘Why on earth did they start another tariff before the old one ended? I had assumed it would start from July 1.’British Gas produced a revised bill at the proper rate. ‘I did not pay them anything until they got the bill correct.’READ MORE: British Gas and E.on customers sent urgent warning over energy billsBritish Gas has now resolved all of her complaints, and refunded money where applicable.On October 15, it wrote saying it would apply a credit to her energy account of £50 “as a gesture of goodwill for the shortfalls in customer service and any inconvenience caused’, and would send a “sincere apology” in writing.Sandra feels vindicated but adds: ‘I should not have had all this aggravation putting things right in the first place.’She warns that customers who do not check their bills risk being overcharged. ‘I will continue to check all my monthly bills from British Gas because I cannot trust them to get them right.”Now she is urging everyone keep a close eye on all gas and electricity bills, regardless of their provider.DON’T MISS:Expert says UK should start rationing now to stop winter energy crisis [LATEST]Millions could receive payment as Cold Weather Payment scheme reopens [GUIDE]Family saw OVO energy bill shoot up to £1.3k a month from £74 [INSIGHT] If you think your energy bill is wrong, question it (Image: Getty)If you spot any discrepancies or information you do not understand, take action, Sandra says. ‘If you complain to your energy company you may be offered refunds and even payments of goodwill, provided your complaint is upheld.’For British Gas complaints contact the customer service team on 0333 202 9802 or write to: British Gas, Complaints Management Team, PO Box 226, Rotherham, S98 1PB.If this doesn’t resolve the issue, you can escalate the complaint by contacting its Customer Services Director’s team via customercomplaints@britishgas.co.uk.If still unsatisfied, contact the Energy Ombudsman.Sandra hopes that if more people take the time to complain, as the combined effort will push British Gas to improve customer service and rectify any errors.She recommends being as precise as possible, especially about billing costs, tariffs and dates.Be polite throughout, but persistent.