Cedars (Hyde Park) Service Issue: Am I wrong?

My elderly parents are visiting and so after contemplating the walk to Cedars in this weather we decided to order in. Went on line to check the menu and found that not only could one complete the order on line, but there was this additional enticement: "10% OFF your first online order! For a limited time only."
I put together and placed the order. No 10% discount was calculated. I called, both to check on ETA, and to ask about the discount. I was put through to a mgr. who explained that this discount had expired and was now only valid if you download their app and use it. "Well then, shouldn't the website be changed?" I asked.
"Yeah. It's 3rd party. They're working on it."
And. . .

Apparently, the mgr. felt absolutely not bound by the unrestricted, unqualified offer clearly posted on the website to encourage online ordering. (Yes it says "limited time," but it doesn't state the limits. One can only assume if this message is what greets you on the website, it must still be in force.)
I didn't argue as I wasn't in the mood to start over with a hungry family in the house. But to me, this seems flat-out wrong.

Comments? Midrash?

It seems so dumb of the manager not to honor the offer under the circumstances. First of all, because he should stand behind what his website says. But second of all, because, what, your total order could have been $40 at the very most? Meaning the amount required to resolve your issue was, like, $4 at the most? He could have taken that out of his own wallet and had a grateful repeat customer instead of one who will likely never bring him business again.

Meaning the amount required to resolve your issue was, like, $4 at the most? He could have taken that out of his own wallet and had a grateful repeat customer instead of one who will likely never bring him business again.

. . .not to mention that it's illegal. I'd take a few minutes to fill out a complaint to Lisa Madigan's office, print it, and mail it. That's blatantly deceptive.