Good evening Sir, I am presently in a state of confusion and really don't know what to do that's why I need your advice.

I am 34yrs old man dating a 23yrs old lady, we have been dating for close to 3yrs now. I am a graduate and presently working while my girlfriend is in her 300level in the university. The issue is that the parents who trained my girlfriend from when she was 5yrs old till now because she had lost her biological parents a long till ago, they insist she must not marry me because I am SS (Sickle cell) but I feel we are good to marry since she is AA but the parents won't allow and they are not given me that chance to speak with them on phone even when i have pleaded so much because both parents (not her real parents) are residing in Canada. My girlfriend and I have seen my girlfriend grand mother and Aunties to express what the situation is on ground so they can talk to her parents on phone since they are not given me the chance to speak with them. I am not sure if they have spoken with my girlfriend parents or not because each time I asked her about it, she doesn't give me a straight forward answer. I feel she feared her parents so much and she is finding it difficult to convince them about me. We have been dragging this issue since over two month now and I really want to get marry this year, she is aware of this but just scared to convince her parents. I am 100% sure she loves me and I love her too. People hardly know I am SS except i tell them because i hardly fall sick.What should we do ? Should I give my girlfriend an ultimatum to convince her parents about me so we know if we are progressing or not or what else should we do ? I really need your advise and suggestion. Thanks