Lost Cashback of R1100 on Fuel. Beware!

Been insured with Discovery for over 15 years, decided to sell both cars on my husband's policy to buy 1 new one. On the days the dealer took the vehicles, 28th and 29th August respectively, we called to cancel the insurance - obviously -no hassle and were told we have 30 days to reinsure the new vehicle when we get it to avoid break in cover or change of status. So took possession of the new vehicle on the 6th September and insured it immediately - obviously - no hassle. Now we are told Discovery refuses to pay our fuel cash back on both previous vehicles for August of over R1100 as the insurance was cancelled a few days before the 31st??? WHAT??? We still paid insurance and vitality Drive pro-rata up until those dates but have a 0 % qualification???? No-one told us to keep re-insuring the vehicles (not in our possession) until the end of August as we would be penalised for the full month. It's NOT like all vehicles are only sold on the last day of each month. At the very least the Discovery Insure should re-imburse our Vitality Drive for this month since the benefits are denied. Pro Rata Please Discovery, This makes no sense!