bad service and contract plan not explained

I went to the Vodacom in Sandton to buy a phone on the 24th of April and I informed the sales consultant that I want to pay R399 per month only nothing more nothing less, she said I could take the R399 smart plan contract which comes with data, smses and 75 minutes, so I did thinking that I would be paying R399 only as I had stated. Few days after using my phone, I got smses saying I've exceeded my limit but I was still able to browse the net, I than contacted the Vodacom call centre only to find that my bill was now sitting at R1600!! I asked how come because I wanted to pay R399 only and they said the Smart plan is an open line once data is finished, I did not ask for this and it was not explained to me properly by the consultant. I then went back to Vodacom and asked to cancel the contract and be put on another plan, they said they would send through the cancellation and call me to come fill in forms again, this was last week and a week has gone past with no contact from them. Another problem now is that I am receiving smses &calls from people I do not know requesting to talk to someone I do not know which clearly shows that I am sharing a number with someone! Is the 1600 legit!