If I go to your website and see a big banner with a promo code, you are obligated to honor it.

If you walk into any retail store in the US, the price on the shelf is legally binding. If you forgot to update the shelf tag, too bad, you are now obligated to sell at the old price.

If you advertise a price or discount, you are required to honor such. Advertising fictitious prices or discounts is an illegal scam.

Likewise, if you have some text generator on your site that gives out prices and promo codes, that's your problem. A customer insisting you honor that is not a scammer, they are exercising their legal right to demand you honor your own obligations to sell products at the price you advertised.

So, this is a scammy business trying to get out of their legal obligations to a customer who is completely in the right.

Lesson: don't put random text machines in your marketing pipeline in a way that they can write checks your ass can't cash.