*Messages from Blocked Number Still Coming Through

I get offensive political text messages from an old associate. I get them to both my phone and computer.

The Messages are to a group of people.

I've blocked the sender completely but still get them.

Mac makes it impossible to leave a conversation unless all people in the thread are iphone users.

imessage greys out the leave message option if one user in a group of 7 is android. And both iphone and Mac seemingly have no easy option to block a number/contact available right on their contact.

Why are blocked callers still able to contact people even if they're blocked?

It seems a simple thing. If # 123-456-7891 is blocked, the number shouldn't be able to contact you.

Continuous offensive texts and being held captive to the thread simply because at least one person in thread is an android user? How is that beneficial to a Mac user? (Both my phone and computer are hit with many texts from the same thread each day.)

I've blocked numerous times.

Is there any simple, non multi-step way to block a number?