No 4G access

after getting off a plane in The Netherlands from overseas my 4G no longer works so I cannot receive or send text messages or emails, use WhatsApp or access the internet. WiFi works fine. The phone an iPhone 12 mini, is only 4 mos old and has not been dropped or damaged. I have turned airplane mode on and off, turned off my phone abs resorted to a factory reset - all to know avail. Really disappointed by this. Any ideas how to resolve?