STAGE 2 Melanoma Cancer- One policy pays out and the other is declined? ?

I have been paying premiums to Old Mutual since 2004, for severe illness, GREENLIGHT policies. Never skipped a payment and never had a claim. Until now, a rather severe claim, malignant nodular melanoma. The most severe and life threatening form of skin cancer, with the highest mortality rate and the highest rate of recurrence. A Stage 2 diagnosis is not something anyone wants to hear. I felt safe that going through this, I had the cover from my trusted insurer of over 16 years. Regretfully this was not the case.... I went for a full skin check up on the 1 October 2020. Upon inspection the Doctor found concerning moles and a biopsy was done the following day. One of the moles came back as a malignant nodular melanoma, staged at T2a Nx Mx on my lower right leg. This was a great cause for alarm as this in an incredibly invasive cancer and steps needed to be taken immediately to further excise the entire region. For this I was referred for further surgery. During this surgery a wider excision area was removed while I was under for a long period of time and a pathologist was in room to ensure the surgeon had achieved clear margins after removal. The incision was extensive and invasive (approximately 10cm in length and approximately 5cm into my tissue) I lost a large chunk of my leg but fortunately, the surgeon managed to excise clear margins and the surgery was successful. A week later, I was then referred to another surgeon, who specializes in melanoma patients, for my Sentinel Lymph Node Biopsy. Again I was under and in hospital. Three lymph nodes were removed in my groin, luckily they came back negative for melanoma.

These surgeries can not be considered as minor. I was unable to drive or work for an extensive period. I have since had resulting level 4 lymphedema, as a result of the lymph node removal, and I am still undergoing weekly treatment with an occupational the****** to try and control it. I should not have to tell Old Mutual, how severe melanoma is or can be. The depth of my tumor is within the parameters, as per my policy documents, anything more than a T1a diagnosis is claimable. I should also not have to tell Old Mutual how high my risk of recurrence is. I have recieved a payment for one of my policies, which I am exceptionally grateful for, but not for the largest of the two. The one that would help me not to worry about finances, while I battle to deal with the aftermath and looming return of Melanoma... that is the one that has not paid out and was declined. I can't understand how one policy with the very same wording can pay out, and not the other? I have tried numerous avenues to get answers, I have lodged complaints and queries. I have jumped through numerous hoops to prove my valid claim. I honestly feel let down that this process has taken so long and has left me to try find an outside route to get this claim paid out.