How can I get my girlfriend's parents to accept me?

I'm 19 and my girlfriend is 17. Her sister, who is the same age as me, recently gave me a call and told me that their dad found out me and my girlfriend had had sex. Keep in mind that the whole reason I didn't get this information from my girlfriend is because her parents equate me with bad and so they cut her off from the phone to keep her from talking to me. So this only complicates things further. I am curently away at school right now but I will eventually have to do something about this when I go back home for the holidays. Before all these complications got in the way, her parents and I were on good terms and they were very acceptive of our relationship. But now....well.
ANY HELP WOULD BE GREAT!!!

Well they shoudlnt be angry with your your girlfriend is 17 years old and she can make that own decision for herself. she should be the one that has a talk to her parents about this. Try not to stress things could be worse off. and make sure you thank her sis that was good of her to do that.

I think you should sit down with your girlfriends' parents and tell them they you love her with all your heart.

I think you should sit down with your girlfriends' parents and tell them they you love her with all your heart.

damn bro im having the SAME issue same same situation and everything my thing is my gurls faggot brother pulld up and printed out our aim convos about our sex life and showd them to her parents now they hate me...and tried/trying to cut off all contact between us, her parents have threatend to not pay for her college if she continues to see me, have you done anything yet that got her parernts to like u? I need advice bro!!