No auth for PET scan

My oncologist filled out all the forms for a PET scan on the 10 Oct. This was quite usual because I've been having a PET scan since 2013. I have CUP cancer, that is cancer with an unknown primary and a PET scan picks up any new growths or old growths that have grown. It picked up a new tumor on my back and liver (both operated on) and 1 in my hip, pelvis and ribs which we keep an eye on via the PET scan. On 29 Oct I get a letter from disc asking about dates of last surgery and chemo/radiation. I write back same day with all the details. Calls and text follow. PET scan auth denied because I don't need a pet scan for investigation of bi****y tract. Note there is NO problem with my bi****y tract. PMBs follow with the previous pet scan and a long motivation about why the pet scan is superior to other forms of investigation for my type of cancer. Auth of pet scan denied again cause discovery got the ICD code wrong! Many texts ensued which were ignored. Calls made where disc said there was nothing they could do. My oncologist gave me cell numbers of 2 VIPs at discovery, called them but they did nothing. Went to head office in sandton and they said my oncologist must motivate for a pet scan (that was what the pmbs where for and there was a long motivation there). They actually said I was denied because I need to find something cheaper to investigate what is wrong. Even though my plan financially covers it! I've given them what they want (more actually) but they won't auth it. I don't know what to do now.