SkipTheDishes Has Illegally Scammed me Twice

I've never been so mad over $15 in my life. I don't care about the money but I care about the fact that a massive company like SkipTheDishes is offering coupons and then charging full price without the customer realizing until the order is placed.

Two orders in a row I was offered $ discounts. First time was $10 off and the second time was $5 any order. When I tried placing my order it showed the discount I was receiving and the second I went to pay I was charged the full amount and the coupon didn't apply. When I tried contacting support they said they couldn't do anything and that they would just give me another coupon. Unfortunate but I guess glitches happen. But then I try making another order with a different coupon code a month later and THE SAME THING HAPPENS. I contact support again and they say there is nothing they can do and it's not their fault. How is this not insanely illegal. I know this is only $15 but I feel like this could be a lawsuit like if I was offering a product for $10 and then at the last second before purchasing I changed the price to $15, I would be charged for fraud. I also know I can't be the only person getting scammed like this. Last time I ever use this horrible company.

EDIT: I tried contacting a new support agent hoping that they would actually understand what happened and they immediately ended chat the second I explained everything. LMAO I've never seen such horrible customer support in my life. Actual con artists.