Extremely disappointed in information given.

a month ago I went into the fourways mall branch to upgrade my cellphone. the sales consultant was extremely helpful. I received my first monthly bill being R1900 more than what was explained to me. I called the call centre and asked why I was charged so much more than what was discussed originally. I was then told there was a migration fee to change my contract when I was upgrade. I fully understand this but what really made me upset is that I should have been told about this fee as we are not talking about a couple hundreds rands we are talking about almost R20000. this should have been disclosed to me when signing the documents that day. when I spoke to the manager I was told there is nothing he can do for me besides change my contract back to what is was to avoid this fee. I am really not happy about this as this is not how you are meant to do business. if I had known about the migration fee I know I would never have changed to a different contract. I am not prepared to go back to my old contract and neither will I be ne happy if I am liable to pay this migration fee. this is not the first time Vodacom has disappointed me. I want this issue solved and the fee waivered .