Booster Bundles

I upgraded my contract with MTN and I asked them to include an additional booster bundle on my package as the contract came with very little data. This was back in February, however around May I called the call center and asked them to take off the booster bundle. So from June until today MTN has not been giving me the additional data. However the problem was that I didn’t check my invoice every month I just continued to pay, a week ago I decided to check the invoice only to find out that MTN is still billing me for the additional data even though I am not receiving it. I have made countless calls to MTN and I keep getting reference numbers and they don’t want to credit me. The close the case without giving me the outcome of the investigation.