Poor customer service Cell C

I have a contract with cell c for data bundles. By merely changing my sim card to another phone it got crashed which required me to buy a new sim card to do a swim swap which I get to be charged again. I didn't like the service I was rendered. This month's data which I paid for I couldn't use because apparently the required sim card to do a swim swap I can't buy it at any shop like other sim cards.very poor service I have ever received if you about to start a contract with Cell c think twice ????????????????