Late payment/default advise needed please

Kesi

Hello. Brief history. Loan taken out in 2010 for online training course. They went into liquidation 2011.BPF did not find like for like course in time. FOS sided with BfP. 1000's of students involved. My account was frozen and remaind so until this year, reason was the miss selling of the course. No letter giving reasons for account being taken off hold (although they say one was sent but they have not sent a copy as requested) and many many attempts from me to find out as too why they should do this in such an untimely manor have failed. Now they are going to put a default on my file -3 missing payments. No payments has ever been made to them. Is there a time limit on how long they can keep a complaint open. It will presumably be another 6years until it's off my file. My credit file showed U -unknown for 5years and except for this it was very good and we were to try for a mortgage this year.