Pathetic service and error correction!

I "upgraded" my long-standing MTN contract in January 2018. The contract was sold to me as a R699 per month contract with a 2 month payment holiday, therefore R699 x 22 months effectively. The first 2 months I expected a zero invoice as I did not exceed my allocated free minutes/SMS's/Data. The bill I received for the first 2 months had a discounted amount of R249 and a charge for itemised billing fee of R21.50 which I was not paying prior to the "upgrade". I went to the Newton Park, Port Elizabeth branch of MTN on 22 June 2018 to complain and demand the credit of the remaining R450 for 2 months, plus the cancellation of the itemised billing and refund of the months charged to date. I got a reference number SMS'ed to me. A month later a received another SMS to say my query had been resolved. But no correction was on my next bill. I then went back to the MTN branch and explained the whole story again. I have now received my next account and all that has happened is my itemised billing has been cancelled going forward. I still want a credit for the R900 overcharge for the first 2 months of the contract and the R172 of unwanted, unsolicited and complained about itemised billing charge. How do I go about this, because it seems that going to your branch and already wasting 2 hours of my time achieved nothing!