Why won't Cox honor an internet upgrade offer I received?

I received an email from Cox that offered me two different upgrades to my current internet package, but when click on the link, the only offers I get are the standard rates, not the rates that were in the email.  I called customer service, and they do acknowledge that I received this email offer, but are telling me the upgrades shown in the email are not available for my account at this time.  They don't give me any reason why they aren't available and they say there is nothing they can do about it, and to just try again later.  The offer has an expiration date of 12/31/2025 and the customer service people don't seem helpful at all.  I also went to the Cox store to see if maybe they could help me with this, but they basically said the same thing.  They also saw the email offer, but couldn't explain why it wasn't available for my account.  I'm not sure what else I can do.  Has anyone else had this kind of experience with Cox offers?  If so, were you able to get any resolution?