My girlfriend denying to marry me after 5 years of relationship

Sir, me and my girl friend were in serious relationship for 5 yrs. We had physical and emotional relationship. She used to come to my home several times. My family gave her soo much love and live like their daughter. Her mom, brother, sister all knew about our relationship for 4 yrs. Now suddenly they kept her mobile and force her to refuse the marriage with me. And now she is also saying that whatever her parents will say she will do. She has been brain washed by them. If i put a case against their parents for forceful marriage she will definitely deny that she has no pressure. Plz suggest me what can i do legally now. I have all the proofs.