DH and I have been married 3 years. I have three adult daughters and two teen boys. One prior marriage. He has four adult children. Two prior marriages. My 24 year old stepdaughter and I get along well. My 26 year old stepson gets upset that his dad won't give him money or just let him move in without discussing it with me. Says it is none of my business. He says if he gets married, he intends to exclude his wife when it comes to his daughter. He has had several run-ins with the law and sad to say his mom bailed him out numerous times.
He refuses to even acknowledge his father's marriage to me. When he talks to his dad, he refers to me as "your girlfriend" or "your old @#! (synonym for donkey, I won't use profanity on the forums) lady." I find this rude, demeaning, and disrespectful. And I can't pretend it doesn't hurt. I don't expect to be called Mom, but I do want my role in his dad's life acknowledged.

What is your husband's response to his son when he talks disrespectful about you?

Were either of you married when you met?

So what is your husband doing to stop this disrespect?

He and SS are not in contact right now. Son blocked us both on social media and we don't have his number.
Hubby did tell him he had no right to insult me.

Good for him! That is exactly what your husband should have done.

Look, this guy is treating you like car but you can't actually force him to stop and acknowledge you. The best you can do is avoid him and your husband to tell him his behavior is unacceptable. If those things have been done, there is nothing else.