Sim not working

[Wondering1]

i tried to change tariff. A new sim was sent, but the old was still working, so I didn't touch it. Tonight, the old sim stopped working without warning. Have switched in new sim, but phone says No Service

[Cleoriff]

@Wondering1 

Keep rebooting your phone.

If still not working then contact O2. You can borrow a phone, use a landline or contact via Skype

All numbers here Guide: Coronavirus Community Help and Support 

0800 587 4005 is the best one to call.

[MI5]

@Wondering1 

If a sim swap has started you need to keep rebooting the phone with new sim in it.

But it could be that your old sim has just failed, in which case, you'll need to contact O2 for a new one. 

The best number to get through seems to be
0800 587 4005