WORT SERVICE PROVIDEr

This is the worst network service provider, for almost 6 months now i don't get calls properly, people only get through to me after the 4th try, my phone most the time doesn't even notify me someone tried to call me. then the last 4 days my phone says emergency calls only. I called customer care and they said i must buy a new sim card and go get a sim swop by the shop. which too me makes no sense, i am paying a contract monthly for only just over a year. never in my life have i had to get a new sim card for nothing. I just feel like they just eating my money and i get the lessor end of the stick because more than half the time i have not been able to use my phone to its full capacity.