What would make a parent be this disrespectful?

Just b/c she's ur mother does not give her the right to treat you that way. You drove all the way there and got treated like scum. Stop trying to contact her. Deal with the fact that she doesnt care about you, get therapy, whatever. Forget her, you try to be a good mother and dont let this woman ruin the rest of your life. You seem to have a really good heart, and she's taking advantage of that.