Unable to send/receive calls, can still send SMS. Phone recognised as 'UNKNOWN_SENDER!'

Thanks for your assistance @andewhite 

Tried those checks and the problem persists, no mobile network at all.

I went to call settings and was prompted with a network / sim error

Sim seems fine, it’s a replacement I ordered a week or so ago to try and fix the errors

Getting a network / SIM error suggests the replacement SIM might not be activated, @Connor K Silo. 

You can do this online at https://my.idmobile.co.uk/activate-sim-outside.

Activated the sim as soon as I got it, received the confirmation text suggesting everything was fine though nothing changed, still no mobile network. The coverage checker tool suggests that my area should be absolutely fine also

Unusual for a physical SIM activation to happen immediately, @Connor K Silo. 

Perhaps there’s a network fault in your area.  

Thanks for the help. I’ll ask about this

You can check for network faults online, @Connor K Silo.

Enter a postcode at https://www.three.co.uk/support/network-and-coverage/coverage.

Hi @Connor K Silo 

Are you getting any bars of signal while using the replacement SIM?

If so, it’ll be activated.

If not, it may still need activating.

Tom