iPhone 11 call drop outs

I’ve been having continued call drop outs with my iphone

I've pursued with my carrier & we’ve done all troubleshooting so now it’s down to the phone

ive upgraded to iOS 15 as I read that may be a solution

it’s still happening

I run a business so it’s a bad look.

my phone is just over 2 years old so I guess it’s apple’s way of forcing an upgrade

does anyone have any solutions I haven’t thought of??

much appreciated in advance