Dotsure use fineprint to not pay a legitimate claim

Hi I am a 70 year old person with a 2018 Ford Ranger bakkie. Km is 155 000 and it is clearly out of its normal warrantee period. Dot sure contacted me by phone more than a year ago with an extended warrantee offer. Obviously I am interested and take out the insurance on both my vehicles R 398 /m each. I am conscious regarding maintenance and preventative maintenance of buildings and moving assets like my vehicles. Therefore my service record is perfect and each visit at the set km stamped in the car booklet. That is even after the normal warranty expired When I recently thought I heard a faint noise at the back of my Bakkie I arrange for a visit to the Ford dealership workshop for a check. They did a diagnostic and found the differential bearing may be the culprit, The oil sample shows fine metal bits indicating a failing bearing. Therefore my preventative maintenance succeeded in preventing a major distress forming. I contact Dotsure and after much hoop jumping they go the diagnostic analysis, my service record and other information required. I am happy because the brochure provided states differentials are covered at various cost brackets based on total km on the clock. Now I give permission to repair the problem under the impression this is obvious that a differential should not start breaking up after merely 150 000km. After handing in the Ranger for the repair and work already done I get a phone call from Dotsure. They record it and they tell me the application for the claim is denied, rejected. Reason it is normal wear and tear and if I have a problem I should read the insurance policy again. Now I would think something like a differential breaking up must leave small metal parts in the oil as it shows it is starting to disintegrate. Suddenly this process is defined as normal wear and tear. I just don’t understand how a preventative maintenance action on my part can suddenly be defined as normal wear and tear. The insurance sold to an older person like myself was accepted in good faith and not been alerted to all kinds of fine print that would allow Dotsure from making a contribution to the repair. I believe this is misleading selling done in a situation where it was accepted as a form of insurance to help a pensioner to at least cover any possible major expenses with his car. It seems this wear and tear as normal deterioration is taken as their escape route to not pay. If I was doing something strange and trying to hoodwink Dotsure to pay for it I would understand, but this, as explained, was all done with a legitimate claim just to find fine print to get out of a preventative maintenance situation. In short, if I did not pay the approximately R800 per month for insurance on my cars for just one year I would have saved enough to pay for this repair myself in any case. Therefore for more than one year I was kept in a fool's paradise I am covered for all major repair works.