United healthcare questions

Hello does anyone else out there have UHC for centura health. I am really confused right now. Right after my doctors office submitted my paperwork I got a letter, which I thought was my approval letter staing I was eligble for surgery as long as I met centuras requirments, which I do. Anyways my Dr's office has never reciverd any type of letter, though they don't seem to concerned about that. Well a couple days ago I called my insurance to see if they had sent a letter to my dr's office yet. Well they told me that I did not have anything up for pre-determination. They did have knowledge that I was having Gastric bypass, but said that this procedure does not need pre-determination, and that if my dr's office needed a letter I could just give them mine. Well now I am confused. What is pre-determination? Is this the same thng as approval? Have I been approved or not,a nd do I even need approval? Please any answers would be helpful, as I have a hard time gettin through to my doctors office to ask them any questions.