Overcharged

I renewed my contract at the end of December. I took out a contract that gave me 120 minutes of free calls and 300 MB data on a top-up. If I used up my data then I was supposed to have to purchase more data. The contract was for +/- R650/m. I was billed R2800 for January. Apparently my new contract was only activated at the end of January so I was given no free data and was charged at R 1/MB. My previous contract had unlimited data so if my old contract was still in place why was I billed for data at all for January? Apparently, I was told when I complained, that this is Vodacom standard practice and appears like a clever scheme to overcharge clients when upgrading their contract. I lodged the complaint on Thursday last week, 3 March, and to date nobody has got back to me. I resent the query on Monday and still have heard nothing.