R198 account accumulate to R11000.00

I would like to know if MTN have any input in contracts that are issued by Autopage? Or does it not matter as long as the products are sold. We had a laptop contract at Autopage and the cell supplier was MTN. After the contract expired, we renewed the data contract and paid R99 per month for 2gb. In September I gave my son the laptop to use and what a surprise we got!! End of October we received an account of R11000!! Apparantly the data was unlimited. If we were willing to pay R99 per month, why on earth were we not told that the data was unlimited? In three and a half years we never paid more than we should, and never used more data than we received every month. The sim card was destroyed, obviously!! And we still have 3 months remaining on the contract. I will never take out any contracts with MTN of Autopage again.