Have you got mobile data turned on? Try searching manually for another network, save and reboot the phone.
If that doesn't work call O2 tomorrow and check that you haven't got any roaming bars on your phone. All numbers in this guide. Guide: Coronavirus Community Help and Support
*The Game Is On*
If using an iPhone, change your data apn to "mobile.o2.co.uk"
Track usage, upgrade and get support with the My O2 appDownload My O2