Incorrect billing

I activates international roaming before I left to USA in June but than decided that I will not need it and deactivated it before I left for some reason it was still active and got charged, upon my return I called vodacom and they resolved this issue and made sure that on there system the roaming is deactived and credited my bill for June.

I receive a Bill for July and vodacom is still billing me for international roaming buy they confirmed that there was a error on there side and that its deactived and I won't be billed yet I am still been billed ,I called vodacom nemourous times for assistance every time I get told that there system is slow and that they will call me back I am yet to receive there call.

Can someone from vodacom please assist with this as I am being billed unfairly and the international roaming was suppose to be deactived in June already.

Please assist