S25 does not receive calls.

[TJHAJH]

Callers to S25, receive unable to connect to phone message. Network strength is good 

[jonsie]

If possible try your sim in another phone to see if it still doesn't connect 

If not visit an O2 store and ask for a replacement sim

Take photo ID with you

[Enlli]

Check 

• Call Barring/Forwarding: 

  Open the Phone app, tap the menu icon, go to Settings > Supplementary services, and check if any call forwarding or call barring options are enabled.