UberEats 20% promo code is a lie

UberEats is so overpriced. So when they gave me a 20% discount code for being a loyal customer I was grateful. When I app**** the code to my order of R321 I only got R60 off (should have been R64.2). This is only a discount of 18.7%. this is before they charged me a service fee, a delivery fee and before I added a tip. I don't understand why you would lie about the discount to make an extra R4.20 hoping that I wouldn't spot it. This business is clearly only worried about their bottom line and has no morals. Ill just order on Bolt eats from now on.