how do i get a replacement sim ?

I can't make our receive calls when at home but messaging works fine , I've tried with wi fi on and off ,I've checked network coverage on mastdata but no data for where I live . Everyone else in our home has no problems,  but they are all on different networks. Haven't tried sim in different handset yet , but would like a replacement  sim to rule that out, but don't know how to get one

Thanks