Discovery Vitality Drive Cashback a LIE

In November 2018 I notice my cash back was incorrect there were fuels purchases that were not included in the cashback calculation and when I queried with Discovery I was told they cannot help me because I do not have slips to prove such purchases even though my bank statement reflected such but it served no purpose as it was not the pint out of the petrol card. I Accepted that and learned my lesson and started keeping receipt from that point and for the past 4 month Discovery Vitality Drive has been providing incorrect cashback and the have show no interest in having this problem solved every month we have to call and query as to why the cash back is incorrectly allocated and the only response we get is that we should upload slips and they reset the amount which is only paid the following month together with the cash back for the current month which is INCORRECT also. This goes to show that they don't care and they are making no means of resolving it and the question is how many people are being cheated of their cashback and they don't notice. I was once informed that my card is not working properly but there are 3 people in my family insured with Discovery and we are all experiencing this problem I don't know if this is implying that all 3 of us have card problem. THIS IS TOTALLY UNPROFESSIONAL AND HIGHLY UNACCEPTABLE, STOP CHEATING CUSTOMERS OF THEIR CASHBACK IF YOU CANNOT KEEP UP WITH THE CASHBACK PROMISE YOU MADE TO CUSTOMERS BE HONEST ABOUT IT AND STOP MAKING EXCUSES.