Mobile data not working on my iPhone

That's a different thing, now that you've explained the error message content.

Start here:--> If you see an Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

If the issue persists, contact Apple Support directly, using this link:--> https://getsupport.apple.com/?caller=kbase&SG=SG003&category_id=SC0999&symptom_id=99976

Regards

Giulio

If you tried (to no avail) all the steps in the support article, then, as suggested, contact Apple using the specific link I posted in my previous reply.

I repeat it for your convenience. Click here:--> https://getsupport.apple.com/?caller=kbase&SG=SG003&category_id=SC0999&symptom_id=99976

What did your carrier say when you contacted them?