We had this problem once with our phone; powering it off and back on again cured it.
You are probably connecting to the internet via your home wi-fi, so the SIM isn't relevant at that time.
You may need a new SIM, contact your provider , if you do , do a back up of your files,photos and contacts to the phone from the SIM if that's possible then you can always transfer them back on a new SIM
We had the advantage of having 2 phones both on the same network, so we knew it wasn't a network problem. It's always worth trying a complete shutdown.