Why can Xiaomi still receive text messages when his mobile phone is blacklisted?

That's your blacklist It's a phone blacklist, not a SMS blacklist.

If your computer supports it, you can also set up a short message blacklist. If you don't support it, there is nothing you can do.

There are two ways to join the blacklist:

1, click on the avatar of the SMS recipient to have the option to join the blacklist.

2. Security Center-Anti-Harassment-Interception Rules-Click the arrow behind people in the blacklist, select Filter spam messages, and add interception keywords.