Often people need to put others down in order to feel better about themselves. Some people enjoy hurting others. These are signs of THEIR shortcomings, not yours. If someone really had your best interests in mind, they would not purposely make you feel bad.

An ex is an ex for a reason. There comes a time when their opinion doesn't matter any more. Let them believe what they want. You know the truth. Be kind to yourself and don't let other's negativity get you down.