You've already discussed this with BF, but nothing's changed? Did you think he has some kind of magic power over his mother?

If you want to continue dating him, develop a thicker skin and don't assume every conversation they have is about you. This kind of friction is present in most cross-cultural relationships.

Be congenial and affectionate toward her, and greet her first even if she doesn't greet you.

Or, breaking up is always an option.