Recurrent Cancer

My father finished his initial treatment two month ago. Apparently, everything was going well til three weeks ago. The radiotion oncologist noticed a 2 to 3 cemtimeter mass on the same location, which is on the base of the neck. My dad was scheduled for a Pet scan; however, he ended up in the hospital due to an infection of G-Tube. The doctor noticed that he was having the same pain which radiated from the ear through the back of the neck. The pain will not go away even with motrin or anaprox. The doctor decided to do a CT Scan to see what is going on. The CT Scan showed areas of concern. The wall of the neck, the tonsils especially, the right side, plus the top of the mouth. The Ent oncolgist was concern with the recurrence so soon. My father was explained what does this mean and the only choose he has. The doctors told me that the only solution at this point is surgery, which my father declined already and won't change his mind. He is ultimately waiting for death to come upon him. If he chose to not do any surgery, then ENT doctors are giving him only six months. As a daughter and health proxy, I'm concern and angry to the fact that the cancer return so soon. Where did we go wrong? What did we didn't do that should have been done? Is it normal to have anger and question God for his action? I understand that people decide what they want to do with their life, but it is wrong to place your children in this ordeal also. People need to understand that treatment and last solution not only affect the patient but also the love ones too.