If you were not advised about this at the time of booking they cannot change it after the fact.

I do agree with the posted that you should just go there and pretend that you had never received the email.

At the time of check out I would write to the charge slip the amount of a dispute and take it with the IHG or CC afterwards.

IMHO I would not loose my sleep about this and I would NOT pay $300 for a substandard dinner if that was not part of the deal when you made the reservation.