MTN -INCORRECT BILLING

Good Day Please can you kindly assist with an issue that i am not getting any resolution. my account with MTN has been billed incorrectly due to the assistant @Foresthill M all in Centurion. She advised that we don't need to cancel the contract as they will charge month to month, we then asked her will the premiums change, she advise no as long as we remain on the contract that has expired already . She then assured us that there will be no problem. We left the store, one month later we received the bill of R1595.00, the original amount was only R500.00, my wife called the customer care, the advise they will check it and get back to us, at the end of this month we received another bill for R1540.00, the query has still not been sorted out. we called in again, with no result, Please can you assist?

Contract Details S Naidoo *** ***

thank you in advance

regards Ivan Naidoo