We can also block contacts stored on the Xiaomi smartphone if desired. Once a contact is blocked, we will not receive any calls or messages from that contact.

Note: To unblock the contacts, follow the same steps in the Contacts app.

Android 10 (MIUI 12.0)
Step 1:  Open the  Contacts app
Step 2:  Choose a  contact
Step 3:  Open the  menu
Step 4:  Tap on  Block
Step 5:  Tap on  OK
  1. Open the Contacts app
  2. Choose a contact
  3. Open the menu
  4. Tap on Block
  5. Tap on OK

Xiaomi Instructions