Hi Pratik_Gaurav,
Thanks for posting in Apple Support Communities! When blocking a contact, it stops them from being able to call you however, you're still able to call them. If you're unable to reach them, they may need to check their contact for you to see if they have you blocked. Blocking your contact on their device would be what stops you from being able to call or message them. Have them check their blocked list:
- Go to Settings > Phone
- Tap Blocked Contacts to see the list
Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch
We also suggest restarting your device, and ensuring the software is updated to the latest version, as restarting and updating can fix many issues.
Hope that helps!