handing over

I have a contract through Nashua which is no more and upon going to the MTN stores I was told one more than one occasion they cannot pick up my number and not to worry. Only to find out a few months later I have been handed over. No warning...yo my knowledge. I have paid up the amount as this is negatively impacting my credit score only to be given quite few numbers but no actual resolution. These people have no sense of urgency and they messing with people's lives. All I ask is for a paid up letter to clear my name on credit bureau...but all MTN seems to be interested in is the fact they have been paid. Please treat as urgent as it is personal and *********** store staff have no clue how to assist as they all give different stories.