sim swap

I am unhappy that I a have to pay R250 to keep my number,the call center agent told me today that I should have told them,when I was ordering the phone. I order the contract phone telephonically, the call center agent I spoke to,he never ask me or told me that if I want to keep my old number to my new contract, which would have been done for free, when I called and requested to have my prepaid number converted to my new contract, I was told it will cost me R250, which I do not have and I feel that I was not informed sooner for me to choose,please help.