Flexi Club - incorrect blacklistin customers

I need help please. Flexi Club did not allocate my debit order last year 7th October 2024 to my ***. I received during April a statement showing that I owe them money. I phoned on the 21st April and was telephonically insured that it would be rectify. Never checked again, never received any more statements. When I app**** for a credit card in June 2025 it was declined because I was blacklisted!! They did inform Xperian which took me off the blacklist, but my history is showing that I was recently behind with 5 installments to Flexi Club. I still do not qualify for the credit card because of that. One does not get hold of Xperian via telephone and I do not receive any mails back. Surely Flexi Club must have a contact person there, but they are telling me I need to follow it up with them. No joy from Flexi Club or Xperian. Really very bad customer service. Quick to backlist you without even making one phone call and now I am fighting a losing battle.