I don't think this will really help much, but I'll give it a go.
Although you are the one suffering, this is really your Mum's problem.
She may well be totally unconscious of what she is doing, but she is in the wrong.
Sometimes the explanation for this sort of behaviour is resentment. Not of you, but resentment that perhaps her life has not worked out as she would have liked. Some mums feel like this and blame their children for it. Some split the blame between all of the children , so everyone has an uncomfortable time, others focus on one child as the one 'to blame' for the unsatisfactory life.
If this is the case with your Mum, it is highly unlikely that she will admit it , or at least not without a lot of therapeutic help.
What you must remember is that you did not cause this situation and should not blame yourself in any way for it. You have done the right thing in trying to bring it up with her and you may wish to try again. However, if she does not respond, do remember that this is her problem, not yours.
My advice to you would be to try to see your Mum in a different light if you can. She is a person with problems which she is dealing with very badly. You cannot help her with these problems, so don't beat yourself up about the situation.
If you try to stop expecting her to be fair to you, it helps a bit as you are not so disappointed when she is unfair.
Keep the communication channels open if you can, accept the situation as much as you can, find other people who value you and accept their valuation of you and remember above all, you are not the one at fault.
Good luck,
:-))