MTN & SSDA RUINING MY CREDIT

Since last year February I have been trying to get *****ulent transactions cleared with MTN. After much frustrations and ups and downs to MTN stores and the police, I was told that everything was cleared up and I received a letter from MTN confirming this, and clearly stating that the collection file had been closed and their debt collectors informed . At that point I was happy with the way MTN handled the situation. However a company called SSDA is continually asking me to pay my non existant account. I went back to a MTN store who then checked and told me I owed them nothing so I should not worry about it. However, I am still getting calls and messages from SSDA who told me that MTN has handed me over to them. Why has MTN not instructed SSDA to close the file? After more than a year, how does this get sorted out and what about my good name that has been pulled through the mud?? Who is actually in the wrong here, MTN or SSDA?