Refund due - Contract cancellation never processed

Cell Phone no. *** - Last year 2015 our contract was due for its Bi Annual renewal/upgrade. We made the decision to no longer continue with the contract and requested MTN to terminate the contract, but transfer the number as such to an prepaid method. In this time period of an month we were under the impression that the cellphone is no longer on contract and therefore would receive our last month's billing. To our surprise 2 months later we were still billed for the as if it was on contract. We once again got in contact with MTN's very helpful call centre (Not) just to be informed that there is no record of this contract being cancelled. Long story short we finally got the contract cancelled with an agreement that there would be an refund due to us, till today after speaking to almost 11 call centre staff we have not received our refund. It is almost a year since the cancellation of our cellphone contract and we are no further in receiving our refund that is legally due to us. I find it unacceptable that we have to beg and plead for our money, we currently have another 3 existing contracts and are in due course due for upgrades and they will not be upgraded. MTN failed