on 01-04-2020 11:14
on 01-04-2020 11:16
on 01-04-2020 11:17
Have you checked for network issues O2 Service Status ?
It could also be a phone or sim fault. Try your sim in another device to see if it works or not.
on 01-04-2020 11:17
You have to persevere with CS. Try Skype
You could try Skype on 0800 032 1402 if the usual numbers are busy
https://community.o2.co.uk/t5/Off-Topic/A-Guide-To-Skype/m-p/1305104/highlight/true#M181823
Veritas Numquam Perit