iPhone X - phone call cut after 6 seconds

Hello uwais98.

Welcome to Apple Support Communities.

If I'm understanding correctly, since updating your iOS, you have noticed that when receiving calls, they drop after a few seconds, then stay connected after the second attempt. I will be glad to assist.

Let's try the steps below to see if it helps from this resource:

If you can't make or receive calls on your iPhone

"Remove and reinsert your SIM card

If your iPhone has a SIM card, remove the SIM card, then reinsert it.

Check your network settings

1. Reset your network settings. Go to Settings > General > Reset > Reset Network Settings. This will erase all current saved settings, including Wi-Fi passwords, preferred networks, and VPN settings.
2. Try to make or receive calls in another location.
3. Switch to a different network band. Go to Settings > Cellular > Cellular Data Options > Enable LTE and turn off Enable LTE, 4G, or 3G (this option will depend on your carrier and device model).

"

Cheers.