How do I deal with uneducated parents?

I've had pica for almost 6 years now. I've been eating chalk and dry wall behind my parents' backs. I got caught on the act 4 years ago. Ever since then, my parents think I'm getting high off of drywall and chalk. They've taken me to doctors, and we found out I have severe iron deficiency. I have done my research, and I know that pica is mainly caused by iron deficiency. But my parents don't know it does. I have tried explaining it thoroughly to my parents, but they're misunderstanding me and / or refusing to understand me or my situation. The doctors didn't tell them much because our advances in medicine are poor in my country. I have told my parents I need iron supplements and vitamins to support my health and stop my habit of eating inedible things, which they didn't understand why i would need them. They think that I can just stop whenever they tell me not to eat it. I have tried suppressing, but it just doesn't work. The worst thing is, they refuse to understand, refuse to look more into pica, treat me like a drug addict because I eat chalk, and have stopped treating me as their daughter. They also blame my fatigue, cold hands, and feet, pale skin, dizziness, and low stamina on the things I eat. Those are all the symptoms of low iron. I just want them to understand. What do I do?