request to extend visa in china.

My name is Robel Girma. I am now in shijiazhuang kidney disease hospital. I came here for medical treatment with my friend. His name is Birhanu Kibret. He is here to accompany me. I didn't finish the treatment in the hospital and we wanted to extend our stay permit for five days. We are asked to get a letter to bring a letter that tells we are friends. Can you help us with this?