iphone 7 sound issue on calles

Hi,

After updating my iphone 7 to ios 11.3.1 there is no sound when I make or receive phone calles, also the speaker icon is greyed out during calles. The sounds is working fine on other apps e.g youtube, facebook, music. This issue happens only during phone calles (both on cellular and VoIP apps such as what's up or Viber), I even connected pods but same issue no sound only on calles.

I tried all kinds of trouble shooting, tried Hardrest, restore factory settings, restore phone backup, still same issue.

This is definitely due to the new ios update, as my phone was perfectly fine before this update, please could someone help!!