Hi
I'm Pradhumn
As, we all know that the cellular network which is the core of our smartphone is very important for us. But if that network goes down or some issue with that, we can't do anything.
But here are some troubleshooting steps by using this you can fix your network issue instant.
Follow these steps to fix:-
Go to settings/ connections/ mobile network
1. Turn on Data Roaming
2. Turn on VoLTE calls ( for HD Calling)
3. Set Network mode to Auto Connect in Both SIMs ( for auto switching different networks in 2G/3G/4G if available)
4. Reset APN settings to default
5. Set Network selection mode to automatic
6. If you're not using private DNS then set it to automatic.
7. Now turn on/off Airplane mode to apply these settings.
8. You can also restart your device after completing step 7.
If the problem still available then
Go to settings/general management/ reset/reset network settings (do it 3-4 times)
Bonus Tip:-
1. Don't use WiFi Calling if your network strength is good.
VoLTE is still far better then VoWiFi
2. Always insert your SIM card in slot 1 which is used for Internet service (don't forget primary slot is primary)
3. If you are using 5G and always in 5G area then select 5G only mode to use better 5G network.
4.If your device is showing Data Warning
Go to settings/ Connections/Data Usage/Billing cycle and Data Warning/ Turn off Data Warning
Note:- I have listed every possible steps to fix. But if any step is left or your know any other method, feel free to comment. It will be appreciated and if works then it will be edit on post.
Thank You
Have a Good Day
See this, in my phone wifi calling is working with Jio 4G 
