Welcome to our Community and thanks so much for your first post; sorry that you're having some issues. Before we can send you out a new SIM, we do need to go through some checks with you to see what the issue is.
So - you advise that your SIM has stopped working? Can you elaborate on the issue? Are you getting an error on your handset at all?
Can you make or receive calls? If people call you, do they get an error?
Have you removed the SIM and tried in another handset at all?
Please do pop back with as much information as you can do we can assist you further.