Unsatisfied customer

I am terribly dissapointed with MTN and their service, I had a contract with them a few years ago that fell into areas, I was handed over to a collection agent named Saya recoveries, I did make the payment outstanding in full to them and I received a paid up letter which I forwarded to MTN and till date they have not updated it, I followed up a few weeks ago and they still saying I owe them money.

Honestly this is terrible service and it is also affecting my ability to apply for credit, I need compensation from MTN for the inconvenience they caused me over the past 4 years.