Omar Khalid says a mistake by his broadband company Virgin Media damaged his credit score for years and cost him thousands of pounds.
"The effect it's had on me has been significant. I can't tell you how much stress, how much anxiety is there for me on a daily basis."
Virgin Media has apologised and says it intends to work with Mr Khalid to "find a resolution".
This all started back in early 2018 when Mr Khalid cancelled his broadband contract.
He wasn't immediately able to send back some equipment so was marked down as being £40 in debt.
Mr Khalid paid the money on condition that when he was able to send the equipment back a few months later, he'd get his money back and Virgin Media would remove the debt marker on his credit file.
So, as agreed, a few months later he sent the equipment back and got his £40 refund. But Virgin Media didn't update its database which meant Mr Khalid was still recorded as being £40 in debt and his credit score got very bad, very quickly.
It wasn't until nearly a year later though in June 2019, when Omar noticed his credit card and overdraft limits had been cut by thousands of pounds, that he discovered something had gone wrong.
'Extremely high' rate
"I've always kept a very close eye on my finances [but] I feel like... I've been questioned by a big company like Virgin Media that I've done something wrong and that's not the case."
He called up Virgin Media, it realised its mistake, apologised and said it would update databases held by credit reference agencies straight away which would fix the problem in just a few days.
But that didn't happen. And in the meantime Mr Khalid's credit score stayed poor, which became a serious problem when he needed a £10,000 personal loan for some home improvements.
He was charged an "extremely high" rate of 24.9% "due to my poor credit rating", he said.
"In the middle of all this my wife and I bought our family house and... we couldn't [make a joint application] because I knew my credit rating meant we would have been declined."
Omar estimates he'll have to pay an extra £3,500 in interest payments because of the interest rate of his loan, compared to a more favourable rate he would have likely got if his credit score hadn't been damaged.
When his credit score still didn't improve Mr Khalid called Virgin Media a further three times over the course of the next year and each time Virgin Media said it would update its records and the problem would be solved in a few days.
But Money Box has discovered that whilst these manual updates by Virgin Media did go through they were overridden each time by automatic updates that were sent each month.
It wasn't until April 2020, nearly two years on from the original mistake, that it was finally corrected and Mr Khalid's credit score began to recover.
"I'd never have thought just a £40 default could have created such a huge impact.
"My finances in the past have always been in order [and] I believe firmly if Virgin Media have made a mistake they should put things back to how they used to be.
"It's painful for me to pay [the extra interest charges] that I shouldn't have to be paying for... and this whole thing has had a huge negative impact on me socially, mentally and financially.
"There are times when I get up in the middle of the night and think about why this thing is happening to me."
Helen Saxon, banking editor at Moneysaving.com expert, said in most cases when mistakes happen they get sorted "pretty quickly" with a complaint to the company involved or, ultimately, the Ombudsman.
"[But] it only really takes one default to put you into a poor credit rating and you can absolutely see rates of 25% on loans.
"Every company has an obligation under data protection laws to make sure the data that they hold about each of their customers is accurate. It sounds like Virgin Media has held their hands up here and the data obviously was not accurate."
Helen says there are now free websites that offer people the chance to keep across their credit scores to stop problems becoming an issue before they happen.
"Check your credit reports, ideally monthly, so you pick up anything wrong as it happens. Then you've time to correct it, hopefully before you need a good credit score for that next loan, credit card or even mortgage."
Virgin Media told Money Box: "We sincerely apologise to Mr Khalid for the issues he has encountered with his credit file and the impact this has had.
"After Mr Khalid returned his equipment, we made an error when processing the refund which meant his Virgin Media account was incorrectly showing that money was owed.
"We will now work with Mr Khalid to try and find a resolution."
You can hear more on BBC Radio 4's Money Box programme by listening again here.