Numbers can be (and VERY often are) spoofed. You might be hit up from some bot in India or something; get annoyed and block the number; and succeed in blocking some grandma in Ohio who has no idea her number was even used for that call.
It’s basically a heavily abused version of an office building with lots of specialty areas that each have their own actual phone number that can be called directly; but when they call out, your caller ID just shows the main line for that building, which prevents random people from calling back directly to that office.
Moral of the story: blocking spammers doesn’t do shit.
When they call, just let it ring and go to voice mail then ignore the voice mail, and don’t send any kind of response to their texts.
Your best option is to support the possibility that yours is an old number that’s no longer in use and thus not worthy of even a bot’s attention.