Misinformed billing for sim-swap

I have a contract with cell c, a week ago I had a problem with network coverage for 2 days. It was completely off, I couldn't make any call nor receive a call. I called the call centre on day 2 and I was told that my sim card is faulty I have to do sim swap which I did purchase another sim for that. When I called for this service, I was assisted very well. Surprisingly, at the end of the call I was told by the gentleman helped me that I am billed R50 for the service, it will be added to my account even though the problem was their sim card faulty. I couldn't understand, why I was never informed before I carried on. I did ask and the guy was helping me, he just told me that's how it is , he doesn't know the reason. Can anyone who knows the reason for this billing tell me because I am not happy to pay for something I don't know.