Bad service : sim cards being deactivated by network

I'm so frustrated with Cell C . My sim card just stopped working in August (contract) so I did a sim swap just a month after the swap the same happened without me even putting the sim card in different phones . Now they say I must do a sim swap again and pay R50 again for something I have no control over . This is just ridiculous. So now I must do sim swaps every month my sims just stop working . Couldn't think anything else than that I'm being *****ed by Cell C.