Boxer Superstore Berea

I have a boxer ecoupon for R50 which I'd earned from my previous purchase. Yesterday I sent my son to buy bread and milk with that coupon, which is still valid until the 22nd of Sept. My son was told the coupon is not working on the system today, so they won't be able to do anything. My child was sent away. It is disgusting how such a huge proclaimed superstore could not even honor a R50 coupon. Why even give these promotional coupons if you treat your loyal customers like this?