The support article has most of the answers you may have, but not what happens if someone tries to message someone that has them blocked. You'll have to find that out yourself.
But if you realise, someone is using my phone number to make calls, there are some things you can do to stop them from spoofing your phone number. Tip 1: Reverse look up the phone number You can simply search a number on Google to perform a reverse phone number lookup.