What is the UK equivalent of this? Last year a phone company wrongfully added a credit to my account for 900gbp which I noticed had been there for a while, cla

What is the UK equivalent of this? Last year a phone company wrongfully added a credit to my account for 900gbp which I noticed had been there for a while, claiming I owed for a phone. It was actually an identity fraud issue. I had forgotten when it had happened and never checked my credit scores, but then during the year needed credit and was getting declined so noticed on checking. I contacted them and they flat out refused to remove it essentially implying I was lying. It happened with multiple phone companies at the time and I contacted them back then and they removed it apart from Three. I even contacted Vodafone for my records and they refused to help. I escalated it multiple avenues such as credit agencies and ombudsman and none could help so ultimately was stuck with this charge. I contacted Three, the managers and CEO and was ignored. So I had no other options (perhaps legal route which I know nothing about) and had to let the credit on the account close after 6 years. The time spent on it and frustration was awful.