iPhone 7 plus receiver and speaker not working during phone call after iOS 13.1.3 upgrade

Hi-

I have iPhone 7 Plus . After recent iOS upgrade ( 13.1.2 and 13.1.3) in my phone, I am unable to make phone calls ( including whatsapp call) as neither my receiver or speaker is working while making or taking the calls. At times speaker sign is also getting grayed out. There are so many other bugs in iOS 13 and those are so glaringly visible but not being able make phone calls is a killer! Only bluetooth device works... When you play music from Youtube , phone audio works but it does not work during phone calls....when I went to Apple store, two service personnel worked for an hour, did network reset, factory reset , audio diagnostic test and so many other tests and finally told that your receiver speaker is damaged due t heat etc (Not due to iOS 13... Hmmmm) and you need to pay $200 to fix it. But I can clearly see it is working on the above mentioned situations but not during phone calls. Does anybody have any answer or solution to this? It is so annoying... Can not use blue tooth to make or receive the call always? Can Apple fix it free? I am out of warranty now Regards