Incomming and outgoing calls not working??

I started experiencing not being able to make or receive calls when I'm away from my wi-fi? I went into Cell C offices in Somerset Mall, they advised me on a new or Zim swop witch cost me R50 +, and lost a lot of info on my cell... one week later the same happens... and now no one can help me? I still have 6 months to go before upgrade...