PAID UP ACCOUNT

I took out a contract with MTN in 2011, and later upgraded to another cell phone is 2012/13. I was then ****** in Johannesburg and that cell phone was taken, I understood that since I had not insured that phone I had to stick to the contractual requirements and pay the outstanding amount. I continued to pay the account , until I realized that there was not much movement to the outstanding balance, it would not decrease. So I queried this and failing to receive a response. I stopped paying the account. I went as far as raising this matter with the Ombuds and did not get much joy there at all. MTN handed my name over to MBD (an attorneys company) which required the full balance of R 6,305.13 which I paid in full and forwarded the proof of payment. I then requested the paid up letter so that I can forward to MTN, to no avail. I requested the letter on two occasions, was told it would take 7 to 10 working days(this dates back July) , it's September I still have not received this letter. Today 08/09/2015 I received an email from another Lawyer firm referred to by MTN requesting the same payment. Thus far MTN has really been frustrating me and I feel I have paid way more than I should.