MTN MESSES UP MY CREDIT RECORD

I received a call from an attorney saying that I owe MTN almost R2000. I said I do not have an MTN account and hung up as I thought this was a ****! I received a call the next day from the the same attorney and after researching the number it was a legitimate attorney. I did my credit check for the year and saw there is an open account on my name with a negative mark from a contract that I cancelled in 2013!! I went to the branch I dealt with and on their records it shows that I put my cancellation in on the last day of the contract and that the cancellation was never finalized by one of their staff. I now have a negative mark on my credit record from MTN's mess up!!! I want a letter of apology from MTN and proof that my credit record is fixed!!! I dealt with Dean the manager from MTN Richards Bay who was very helpful, but haven't had feed back which is concerning. This is a serious matter as you are *****ing up my Credit score. Take note I also sat there for close to 2.5 hours which I had to take off of work time trying to sort this. FIX IT NOW!