Message Blocking feature not blocking incoming SMS messages

I’d like to block incoming SMS messages. The “Message Blocking” feature described here sounds perfect: https://www.t-mobile.com/support/plans-features/message-blocking

This part especially:

Blocks all chargeable incoming and outgoing SMS and MMS messages.

I turned the feature on last week for my number here: https://www.t-mobile.com/account/profile/blocking/Block%20Messages/$MY_NUMBER

But I’m still getting SMS messages! More specifically I am receiving spam messages from 10-digit “Longcode” numbers. I can see them in my usage log here: https://www.t-mobile.com/usage/details/messages

Why are these messages still getting through?

How does one find out if a message is “chargable” or not?

Thanks in advance for any help!

PS: I already tried calling support but was not able to get anywhere. It’s incredibly frustrating to try and solve these kinds of issues over the phone because we’re not looking at the same documentation and account pages.