3g download in under 10min

I received a sms on the 1st Nov, stating that my data usage is unusually high and I should investigate. Next message, 30sec later, informed that that I will now be charged out of bundle rates for data usage. Next message informed me that my service has been suspended due to R3900+ data usage. I locked a complaint but was informed that everything is kosher. Going into the Riverside Mall branch to see if they can assist, it came ot light that the 3.9GB in question, has indeed been used, in under 10 minutes!!! I have a Samsung S3 Mini, and I stay in Pilgrim's Rest, Mpumalanga, where reception is poor at its best!!! To download 3.9gb of data in 10 minutes, will take a mirracle in most areas, and on this phone, in this area, is technogogy wise, just not possible. That was the verdict from Jonathan in Nelspruit. Linda, at the call centre though, insists that it is legit and needs to be paid. I am a 69 year old pensioner, and just cannot do this. Please can you assist. I have talked and asked many people about this, and the consensus seems to be that 3.9gb in under 10 minutes is not possible.