I am unable to answer incoming calls. Sliding does'nt work

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

You might not be able to make or receive calls on your iPhone if you have certain settings turned on, if your software isn't up to date, or if there's a problem with your network.

Find out what to do if you see "No service" or "Searching" in the status bar. If you can't make or receive calls on your iPhone, follow these steps, testing after each step:

Check your iPhone settings

1. Turn Airplane Mode on and off. Go to Settings and turn on Airplane Mode, wait five seconds, then turn it off.
2. Check your Do Not Disturb settings. Go to Settings > Do Not Disturb and make sure it's off.
3. Check for any blocked phone numbers. Go to Settings > Phone > Call Blocking & Identification.
4. See if Call Forwarding is turned on. Go to Settings > Phone > Call Forwarding and make sure it's off.

Update your software

1. Check for a carrier settings update.
2. Check for an iOS software update. Some updates might require a Wi-Fi connection.

Remove and reinsert your SIM card

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

Contact your carrier

When you contact your carrier, make sure that:

• Your account is set up to use your iPhone.
• There aren't any localized service outages.
• Your account doesn't have a billing-related block.
• Your calls don't have errors on the carrier system.

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).

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

https://support.apple.com/en-in/HT204027