I’m writing to you as a last resort. In 2014 I ordered a Cashplus prepaid card from a firm called Advanced Payment Solutions. I wanted to use it for holiday spending abroad.

Investigating a mortgage for a new home last year, I found that my credit rating had gone from excellent to very poor. After reviewing my Experian file I could see five late payments of £4.99 registered by APS. This was confusing as the card was a prepaid card only and would only ever hold money that I had transferred to it ... or so I thought.

After numerous calls to Advanced Payment Solutions I found out that it had applied a “credit booster” product to the card at £4.99 per month for 12 months, to build a credit history. This is a product I didn’t need. I informed the company that it had made a mistake and could it please revoke the missed payments and correct the error.

A period of denial and unwillingness to help followed. Call after call and failed callback requests ensued. The financial ombudsman got involved but suggested that there was very little evidence to show that I did not request this product, therefore it could not enforce a retraction.

I work in financial services and must maintain a good credit rating to remain employed in the industry. The fact that the company can apply a “product” to any account without me having signed a contract is unbelievable. MA, Edinburgh

The case shows the problems of using an unmonitored email address when signing up for financial products. The company says it sent you several emails about these payments. You didn’t receive them because you used an old Hotmail account that you rarely looked at.

We asked the company to look again at this case, and it says it is certain that you did sign up for this service and therefore it won’t do anything to help you. “We have an obligation to report factual repayment information to credit agencies, which in light of the evidence we have, would not allow APS to overturn our decision. A decision which was also upheld by the FOS,” says Rich Wagner, APS’s chief executive.

You are adamant you didn’t, and have had your credit score messed up for what is a trivial sum.

Ultimately, if you genuinely believe that you didn’t, and restoring this score is important to you, start legal action against APS, and you may find it changes its tune, although it won’t be cheap. In the meantime, apply to the credit reference agency and get it to put a note of correction on your file to explain the reason for the missed payments. This should help in any future credit applications, given that it is a tiny sum.

We welcome letters but cannot answer individually. Email us at consumer.champions@theguardian.com or write to Consumer Champions, Money, the Guardian, 90 York Way, London N1 9GU. Please include a daytime phone number