Log into your account and click change sim card. Green arrow on picture below.
It will show you last 4 digits of the sim card. Now take the sim out of your phone do they match?
If they don't you have Been a victim of simjacking.
Click plans and add-ons then lost/stolen mark it as stolen to block whoever has access to your account sim.
Then immediately start changing all your passwords and check your financials for fraud. Be sure to check PayPal if you have an account, change that password immediately as the simjackers seem to target that first.
Then open a ticket for moderators to investigate. They have away to get your current sim card working again.
Or private message them at link below
Or your other option for a faster resolution is to go out and buy a new sim card. DO NOT ACTIVATE IT!!. You have to take the brand new sim card and log into your account. Click "Change sim card" enter new sim card number and you will be back up and running.
Let us know!