I used Experian when i got refused credit and it turned out i had a few debts i forgot about. They did have 1 debt wrong though because it didn’t show as being paid, i wrote to them and got it updated.
I wrote to Experian as suggested and they said as far as they were concerned the information was correct and i should speak to Barclays. After a lot of discussions with Barclays it would appear i have been the victim of fraud which i have reported. They are investigating it at the moment and hopefully they find out who it was.