Surplus not paid after expiry of 24 months contact

I had a contract with mtn, 24 months lapsed and I had to upgrade, took handset that's less than the previous one. I had a stop order and didn't change it, so at the end of contact I had a surplus due to me. They wanted me to upgrade again and I requested the contact to be terminated and requested that surplus should be paid back in to my account. I have been waiting since February for my money till today still no payment.

I want my money MtnSA