DATA OVERCHARGED R2600-00 WITH ACTIVE CALL LIMIT

I have a Plan 2GB MBB 24 month - Contract with Vodacom WITH an active call limit of R300-00. My monthly subscription is R109-00 plus the R 300-00, thus my budget fir this is R409-00 per month. I now received an account of R 2919-52!!! When calling Vodacom, I was told that \you must read your terms and conditions. Although you have a active call limit