PRIVATE NUMBER and RIDICILOUS ACCOUNT

On the 23rd of March I upgraded from a Talk 500(BB) to a Red Advantage(SonyZ3)as they advice me that it will the best option. I ask that they must put a limit on my data usage as I only use it for Watts-app few other things.( People warn me of getting high accounts after upgrading). They say that on my contract it is not possible-WHY? I was thinking of a Data top up account or If my data is finish I can always decide to buy bundles or wait for the next month.( With kids around it was a concern)Then my surprise arrive -an account of over R4000. My average account for the past year was about R1100. Apparently I used 3.10 GB from the 23rd of March until the 13th of April. I went to Vodacom in Bloem about my number showing-PRIVATE NUMBER, that's after I called Vodacom and visited the shop. They ask me did I realise how much data I used in 2 weeks and was really surprise to hear that Vodacom Potch did not explain how data work and to buy bundles in time. How to check my balances etc. A lady from investigation/complain departed called me,but was so rude and made such allegation that I ask her to send it tome in writing-I'm still waiting for the email! PRIVATE NUMBER-still no help!!!!