iPhone 13 running iOS 16 suddenly can't connect to mobile network please help

Hi - used my iPhone 13 since new a year ago, happily and without issue. However, over the last 2 days it has suddenly failed to connect to my mobile network, meaning I can't use mobile data when I am away from wifi and also I can't make or receive calls. It connects to wifi without any issue and obviously I can make calls over wifi (such as WhatsApp etc). The only thing that has changed recently is that I updated to iOS 16 a few days ago - however everything was normal for the first few days, the problem only started yesterday. So yesterday I eventually learned of a fix: "reset all networks" - and hey presto, it worked. However....when I switched my phone back on this morning (I always shut it down overnight), same problem, it couldn't find my mobile network. What makes this odd is that all the other members of my household have smartphones (both iPhones and Android) on the same network and they haven't had any problems in connecting their 'phones to the network.

My phone is still under global first year warranty, but I can not afford to lose it to the repair shop for days/weeks, I depend on it for work and everything else.

Does anyone have any clues what could be happening? Thanks