Breach of Contract, Billing/Accounts and Feedback

Approximately 3 years ago we took out a Internet contract with Autopage Cellular at their Key West Krugersdorp Branch for 2 GB of Data which we pay R95 a month. When we took out the contract we asked if it could be capped at the 2 GB, as we have a mentally Challenged daughter who would be using the internet but does not understand how usage works. We were told that it had been done. for the last 3 years we have been charged our R95 a month and all was great. Until in June we were advised while trying to Skype to family that we had gone over our limit and were told to contact our Provider. We did this immediately and when we asked how much we had gone over we were told to the tune of R17 960.66. We called the Call Centre and were told that a sms was sent to our phone informing us 2 weeks earlier about the limit being exceeded. NO SMS was received on any of the phone numbers given to the Provider. We requested that a full billing be sent to our E Mail, nothing has been received to date. With no data available the bill has increased to R20 000+.All our enquiries have been answered by automatic replies even after we requested an answer by phone. and we have been told we have to pay.