MTN will not upgrade contract

I upgraded my MTN databundle on 23 June 2015 from 1 GB a month, with automatic topup, to 2GB a month, without automatic topup. However, MTN did not implement the new contract and continued to enforce the old contract, which was highly disadvantageous to me. Thus, instead of paying a maximum of about R128 per month in terms of the new contract, on 1st August I was charged R2450.14 and on 1st September R1777.68. I have visited MTN's Benmore office several times to try to bring the new contract into operation and obtain a refund for amounts overcharged but, although the staff there are friendly, helpful and keen to assist, nothing ever materialises, and all I get is a new reference number, whilst I just keep getting charged these outrageous amounts. Please can this be escalate to a level where it can be resolved?