Wrong information so they make a quick buck

My contract was finished so I wanted to change to Prepaid until my device could no longer function any more. One the consultants at Vodacom when I called gave me a so called amazing deal where I could get 10 gigs a month. Explained to me that this was not a contract and that I could upgrade whenever needed. Now my device has giving in and I was told that I am looked into a data contract and that I can only take out a new contract with a new number. This is the worst service I have ever received. I want to pay Vodacom R 1 399 for a new contract on my existing number but have been told that this is impossible. I am so disappointed as I totally had the wool pulled over my eyes