Not able to connect to 4G connection

Hello ,

One month back , suddenly my iphone X was started heating and a warning sign appeared on my phone that temperature of my phone is too high and it automatically got shut down , i was not able to charge this phone and after few days , i changed my iphone battery and everything is working perfectly. Except my iphone is not receiving 4G signal and it constantly shows” E “ sign in network bar. I contacted apple support on phone and they ran diagnostics and everything was normal. I have checked and changed my network settings multiple times and even changed my sim(AIRTEL, india) and my network service provider also checked my sim and phone setting and told that my sim is perfectly working and my settings are properly set. There is no Vpn app in my phone, no third party app, i am able to make a call and receive but not able to use 4G service and even messaging service.

kindly help.