Just reading on the BBC website that it appears users of the iPhone XR on the O2 network have had several issues today.
It appears many customers have not been able to get good phone reception, this has been affecting calls, both incoming and outgoing as well as the ability to send and receive text messages.
It also seems that people have had trouble with a data signal, so this would of effected WhatsApp etc.
O2 have said the old classic IT line of switching it off and on again resolves the problem, all be it temporarily.