Infantile anorexia

I have an 18 months girl,her weight is only 7kgm,height 70 cm
She has no appetite, refuses food all the time since birthday, seen by a lot of doctors but with different prescriptions but with no response
Other milestones of development are nearly normal she doesn't,t chew food and doesn't swallow except very very small amount of food.
What to do please
Thanks a lot