Ridicules Invoices, charging for things not agreed upon.

I have a contract with Telkom, for 3 months everything ran smooth and my contract is R490 per month. All of a sudden I received a invoice of nearly R700! They slapped 2x 800mb data on my contract and bills me for it! No way! I have uncapped wifi. If I need data I will pay for it. Now I have been struggling for days to get hold of someone to rectify this! No response via mail or sms or call! I need answers.