I've just upgraded to an iPhone11 and now can't make or receive calls. The outgoing calls all show 'failed' and the incoming calls all get a voicemail recording. What do I need to do to rectify this?
Are you using your old sim or did you do a sim swap if using a new one?
Guide: Sim Swap: a mini guide 2017 update
Track usage, upgrade and get support with the My O2 app