Xiaomi: Block Calls from Unknown Numbers Automatically

Calls tagged as Unknown or Private number arrive without a caller ID, so MIUI cannot match them against your contacts or an existing blocklist entry. Standard call blocking only works on numbers that are actually visible, which is why hidden callers keep getting through even after you block every number you can see.

MIUI has a dedicated filter for exactly this case, built into the same menu as your regular blocked numbers list, so no third-party app is needed.

Open Phone, tap the Menu icon, then go to Settings. Select Blocked numbers and enable the Unknown option. From this point on, every call without a transmitted caller ID gets rejected before it reaches your lock screen, and the caller is sent to a busy signal or your carrier voicemail.

There is one trade-off. Some legitimate calls, such as certain business lines, hospitals, or international numbers, also arrive without caller ID and get blocked the same way as spam. If you are expecting a call from a source that regularly shows up as private, turn the filter off beforehand or ask the caller to use a number that transmits an ID.