sim card faluire no help from cell c

My wife has been along time customer of cell c renew contract for a z3 blackberry now in one jear the sim card has failed and every 3 months and every time its a new sim and have to rica AGAIN we phone cell c customer service and first takes u trought a automated system for like 5 min then u get to a operator ask them to call u back Nothing ,all cell c customers move to VODACOM or MTN it is the worst network in south africa