my iphone 7 says searching and finds no cellular service. I've downloaded the latest software 15.2.1 but still did not fix the issue. I can't delete the update version of ios to download. help

Phone was working fine and then all of a sudden now it shows searching for service. Then a popup says "Cellular Update Failed Your iphone cannot make or receive calls or access cellular data until it has been updated." I updated to the fix of 15.2.1 and it still shows this message. I tried to delete it and update it again thinking it may not have downloaded correctly and can't do that. Any ideas?