iOS Calls Fail

[tonym961]

Hello everyone,
I've an issue on my iPhone 14 Pro with iOS 13.3.1 when i receve a call.
When i'm on Nicegram app my phone rings well and calls works, when i'm on standby or in other app, the call notify will appare for 2 seconds and disappare and if i try to open quickly Nicegram and try to answare, my call go down.
I've tried to reinizialize my phone (full phone and network settings) with no results.
What can i do?
In advance i've checked notify settings, call low data ecc..

Thanks