Forcing me to buy a sim card I dont want or need

I opened a Mr Price account and fetched my new card yesterday. When I got the card I was forced to buy a sim card that I don't want or need, as the store told me it is compulsory with a new account. I didn't even take thew sim but now I must pay for it. WHY??? Why does Mr Price force me to take a new sim card that I don't want or need.