First you weren't right in your girlfriend's eyes, so you decided to break up. Now, as far as your parent's are concerned, you aren't right either. What an awful position to be in. Never right wherever you turn.
Your problem stems from what we call "blurred boundaries", which means that your parents see you as an extension of themselves; they cannot accept you as a separate person. Whenever you attempt to be yourself and follow your heart, they feel insulted or betrayed and accuse you of being wrong. In their eyes, anything that differs from their views, ideas, wishes, or feelings is wrong. I'm sure that this problem with them started long before this business with your ex.
I also have a feeling that your parents have been influencing your decisions and blocking you from making a healthy separation for a long time by using emotional blackmail (cold shoulder treatment or threats of abandonment).
Since your parents think everything that concerns you is their business, they are butting into your choice of girlfriend, which is another example of their blurred boundaries.
I've given you the technical explanation of what is occurirng. Now what can you do? Two choices: Either bow down to them and lose your identity; or stick up for yourself and risk losing their love. The choice is yours. If you don't take a stand with them now, and run this risk, they are going to be meddling in your business forever. The stakes are higher than ever and if you aren't careful, before you know it, they will choose your wife, career, everything.
If you decide to take the risk and confront this issue with them, then one way to go is to lovingly set a limit on their behavior. You could do this by saying: "I understand how disappointed you are that I broke up with (I don't know her name) and I know that you want the best for me. But, by trying to impose your choices on me, I am not being helped to become a separate person. I need you to support me in what I want for myself. If I fall, I fall, but this is part of my growing up. I have to define myself, make my own life, my own choices and my own mistakes. If you keep trying to protect me from making mistakes, I will never be able to stand on my own two feet. Then how will I make it when you are no longer around?"
Then tell them that when they give the cold shoulder to the other girls you date that they are acting out their feelings of disappointment and disapproval. (You can tell them that you accept their feelings but do not appreciate their acting these feelings out.) If they think that acting coldly with your new girlfriends will manipulate you into getting back with your ex., tell them that they are wrong. All they are doing is pushing you away from them. Ask them if they really want to drive you from them. Having said all this, rest your case.
Keep in mind that in order to break free of their rule, you must be willing to risk losing them. It's like a poker game in which the worst case scenario (losing them) rarely plays out, but you have to be willing to play the card. Up until now, your fear of losing them has likely kept you from standing your ground. Little by little, they became "trained" to push you around. (Because they knew you were too scared to run the risk of losing their love, they knew they could get away with running you.) Once you are willing to take that risk of losing them and they sense it, you have broken their hold on you forever. I highly doubt they will let you go. Remember they see you as a part of them. Letting you go would be like killing themselves.
I know how scary it is to take this step that I am suggesting. For years, they have been blocking you from separating with their threats of abandonment, so that taking steps to separate and stand your ground now does feel like you're risking everything. But, as I said, I don't think you could get these people to reject you, no matter how hard you try. As I said, it feels like they are too tied up with you to ever let you go. So realize that their threats of abandonment have been used to keep you part of them, nothing more. Now's the time to politely assert yourself.
If you feel that you need additional help with this issue, please let me know. In any case, keep me posted on how everything progresses.