MTN retention and collection messed up my life

What a struggle!

I paid off my cellphone contract on the 25th of June and called customer care to let them know I will not be moving to prepaid and require the number to be taken down/blocked. The assure me they would but couple of days later I receved an email from CSS Credit Solutions Services asking me to make payment as my account is in areas, I explained I have paid and they said they would ask for a statement form MTN and ultimatly sort everything out. This did not happen, I have since received, SMSes, more emails and calls from from CSS Credit Solutions Services. I have emailed MTN countless times since then and nothing has been done. Worst of all this has affected my credit as it shows up as if I have judgements agains me when doing credit checks.