GAME GATEWAY ROBBING VODACOM CUSTOMERS

Yesterday I visited Game Stores Gateway to take on a new Vodafone contract, however I wanted to convert on of my previous contract numbers. So once the contract was approved, I was asked to pay an additional amount of R105 for a simcard. As a vodacom customer, I am full aware that if you use your own simcard, you don't pay the R105. So the cellphones dept manager was called, Calvin, and I questioned him, he said that rule came from management. I then requested that he can give me a blank simcard and I will pay the R105. He said he can't do that. So I must pay for an item that I didn't receive from the store? Is that not a crime? I questioned him, so if I use my contract simcard for over 10 years, I have to pay the R105 each time I decide to to convert it from prepaid to contract. I am fully aware that other stores don't charge the fee in this situation. Why is Game Gateway robbing the vodacom customers?