Anyone who is calling me is getting busy tone though I am not using my phone too. I changed my SIMtoo but problem is same. I tried my SIM in other phone and it works well. DONOT disturb option is off too so not sure which option to turn off. any help

Greetings ajaysethiiii,

It appears your iPhone has an issue receiving calls. That does sound troublesome. The following article may help you find a solution:

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

Check your iPhone settings

1. Turn airplane mode on and off. Tap Settings > Enable Airplane Mode, wait five seconds, then turn airplane mode off.
2. Check your Do Not Disturb settings. Tap Settings > Do Not Disturb.
3. Check for any blocked phone numbers. Tap Settings > Phone > Blocked.
4. See if Call Forwarding is turned on. Tap Settings > Phone > Call Forwarding.

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.

Update your Preferred Roaming List (PRL)

The PRL determines the cellular towers that your iPhone uses for cell service and selects those with the best signal strength.

• If you're on the Verizon network, dial *228 and select option 2.
• If you're on the Sprint network, dial ##873283#.

Contact your carrier

When you contact your carrier, check the following:

• 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. Tap 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. Tap Settings > Cellular and turn off Enable LTE, 4G, or 3G (this option will depend on your carrier and device model).

Still can't make or receive calls?

If you still can't make or receive calls, restore your iPhone as new.
If restoring doesn't fix the issue, contact Apple Support or take your iPhone to an Apple Retail Store or Authorized Service Provider.

Thank you for contributing to Apple Support Communities.

Best,

Bobby_D