MTN ruining credit rating, I have no account with MTN and they wont fix it

I have no business ort accounts with MTN anymore since june of last year, all my stuff was paid up and no more contracts, MTN is now messing with my credit record saying i havnt paid for more than 3 months, but I owe mtn nothing? I am going to sue for damages caused as I cant apply for finance since my wife is on unpaid maternity leave.