How do you deal with someone criticising your weight?

My dad has ALWAYS had an issue with my weight. I was over weight then steadily lost the weight over a period of 2 years 3 years ago to be more healthy. Weight, self image hasn't really bothered me, but over a long period of time I am a lot more self concious and feel a lot more insecure within myself. Because my dad still comments on my weight. We haven't spoken in years and he still chats **** about me. He has now convinced my sisters to join his little hate party and this is all they ever talk about to me. My 2 sisters are naturally very slim and petit where as I have never been. Even as a child. I just want the talking to stop. Why can't they accept that I will never be as slim as them but I'm taking care of my healthy and lead a more active lifestyle. It's very irritating.