Mtn to please sort this out

I am so tired of how *********** the agents at mtn are.. I have been telling them now for the past year that the Sim card they sent me was not what I was looking for. Instead of resolving my query they decided to debit my account monthly. I have been calling about this but nobody now what they are doing. I resently app**** for a home loan, all the banks are refusing me because I have a default in my name for a Sim card that was never even activated.. How can that be??? I even paid the outstanding balance on contract so that the account is in order. I have even asked for a settlement letter to pay up the account as this delay will make me lose the house I had my eye on.... No body has bothered to assist with this too.. I need someone to resolve this ASAP as this was not even my fault.