Why had Heck Tate not called a Doctor?

I'm not sure exactly what your question pertains to. If you're referring to the end of the story, Dr. Reynold's comes to take care of Jem, and then goes to check on Bob Ewell's dead body. Although initially, the doctor is there to care for Jem's injuries.

I'm not sure exactly why, but I think its because someone else supposedly called Dr. Reynold's to come take care of Jem.