Health Mediclaim is denied without proper reason

Hi, my parents are covered under health insurance.My mother has been diagnosed with Metastatic/Last stage of cancer.All test has been done to find the stage of ailment and 6 cycles of chemo therapy has been suggested by Dr.I have made claim for 1 & 2 cycle of chemo and amount has been refunded. The last cycle of chemo is completed in first week of February, 2016. I did not claim for last cycle of chemo. Later on consultation,Dr. has prescribed the PET-Scan test to know the improvement of treatment for existing disease.Based on outcome of reports, Dr. has started new treatment of chemo medicine. My above post medi-claim of PET-Scan and consultancy has been denied with that reason that it is for the Investigation & diagnosis of the disease & as per policy, company does not pay for the diagnosis of the ailment. As per the documents submitted and reports, it is clearly mention that those test has been done as part of ongoing treatment and it comes under 60 days of chemo completion.But the insurance third party is not ready to accept it because we did not claim for the last cycle of Chemo in February.However all the timelines are clearly mention in the documents submitted. Can i take this case to consumer court? Or can i send legal notice to third party vendor company for denying the claim without proper reason? Please suggest, i will be really grateful. Thank.