Hi, I have private health insurance with Aviva and not had any problems when asking them to cover issues connected with the breast cancer. for example all my treatment was in 2014 and in March this year after struggling with dryness in the vagina I asked if I could see a gynacologist - yes no probelm they said. Also, my liver functions were raised a lot in August after seeing my oncologist - could I see a liver specialist - yes no problem.
Unfortunately my mum was diagnosed with ovarian cancer in Sept 16 Stage 4b 😞 she died Jan 17) because of the connection between breast and ovarian I told my oncologist who asked for a ct scan and again they had no problems.
I dont see why you arent covered - maybe ask them if you get a letter from your surgeon or gp that states the problem is as a result of surgery for the breastcancer, unless there is a specific clause in your policy or your company has a certain level of cover. I would ask them why you are not covered.
Hope you get the answers you need