Living a nightmare

I 'm living a nightmare with Blue Label Connect, I had a contract with Blue Label Connect for 2 year all was fine until I had to upgrade it last year April, that's where my nightmare started. I was given a phone which was not what I upgraded to which I had to return it, the return was successful to my suprise on my bureau profile I started to have arrears on their account and I have called them reversal times to query this an I even got a letter from them but the status remains saying the account is open and overdue to this day and this has blocked me everywhere when I try to apply for credit, since November I have been communicating with them to update and remove the account. All I am getting from them is that it will update in 90 days which is now more than 6 month