Failure to assist customer

I recieved a call from telkom mobile offering to renew my contract and I agreed on condition that they will change the cell phone number which is currently used for my contract to other prepaid paid number. The agent said it would be done all I need is to go to the nearest telkom outlet as soon as I have recieved the phone. I went to the outlet after recieving the phone and they said I can not change my number. They asked me to call the telkom mobile. When u called the agents could not help me either. I am phoned to use a number which I specifically said it should not be used for the renewed contract as the number is not my main number .