DIscovery Insure Petrol Refund not correctly calculated

Does anybody know what is happening at Discovery Insure? Discovery Insure has ignored some of my petrol transactions 4 times in the last 12 months. I had to contact Discovery Insure to get my petrol refund back each time. Why is this happening? Is somebody committing ***** at Discovery Insure? I am 66 years old, but still capable of checking all my petrol and credit transactions each month. Am I a "target" (because I'm older and likely not to check my transactions & refund)? Without the petrol refund Discovery Insure is more expensive than other insurers.