Why is the plan renewal offer in the app not available when you go to renew?

I have a message in my app that states my plan expires in 1 day, and when I called to renew with that 30% discount, $349.30/year for OnStar One, but I was told it was unavailable to me. Why advertise that if you won't stand behind the offer?? That's such misleading advertising and a sketchy business practice.