What do I do if I was charged with theft with the postal service which is a felony?

Are you really asking why your employer, who believes that you stole from them, won't just give you your job back? Since the answer to that seems very obvious, I am going to assume that the question was garbled somehow, and ask that you repost it. (A diversion agreement does not change the belief of your employer). If you are a member of the Postal Union, you can ask your union representative this question as well.