Double charge for data

I am on a smart broadband LTE contract. In July, my monthly allocated data depleted and I recharged on the Telkom website with more data. I filled in my card details and the amount was deducted from my account on the same day. When I received my monthly invoice from Telkom, the amount for the recharged data appeared. The normal monthly payment + the amount for the data I recharged with was debited from my account. I have disputed many times, spending hours on each call for the past month, sending my bank statements to more than 3 people as proof and still no one wants to assist me. I request to be put through to a manager and no one wants to assist. I am really disappointed in Telkom. I've been a loyal client for 4 years, not even once missing a payment. But I'm now being cheated out of my own money.