hidden added costs for keeping old number

I signed up for a new contract over the phone, the consultant was friendly enough, but she told me I could not setup my old phone number (a cell c prepaid number) on the new account at the time, and that I had to call back once I received the phone, so I did and was then informed that I had to pay another R250 setup fee for porting/using my old number, I feel that this is a bit of a **** and should have either been communicated up front if not charged at all.