Loaded 10gig once of data without my consent

Hi. On 3 August I looked at my mtn bill and found i was billed for a 10gig once of data bundle which i never asked for or confirmed that i wanted it. It was loaded on my data contract and i never even received an sms to say it was loaded. They charged met R599 for it and where i normally pay R280 i had to pay R820. I emailed them and they responded on 6 August saying i had confirmed to a once of data bundle of 10 gig, but i have no sms records of it nor any knowledge of it. I phoned mtn to lay a complaint on the 4th of August as i could not get through on the 4th. They had found that it was a lady who loaded it to my account and that they would email her and ask why there was no note of it left on the system. I never heard anything back, on the 14th of August i phoned again to ask weather they had found the problem, the person said they need to find the guy who helped me to find out if he escalated the issue...and that she would call me back. Today is the 26 of August and i have not heard anything. I am supposed to pay the new bill now. Please help me resolve this. Ref numer ***7