Disability Support Pension Appealing

Hi I was diagnosed with triple negative grade 3 stage 2 cancer 2 days before christmas 2020. I have a back injury and have been on the public waiting list for surgery as well as mental health issues. My claim for the disability pension got rejected as they like to say so I am putting in an appeal. I understand you have to reach a certain criteria. I have been unable to work for a very long time now and I would like some advice on appealing this decision. I have no idea how long my journey will be