Diamond rewards Peacock Premium benefit no longer working

I'm a Diamond rewards member, so as far as I was aware, I have access to free Peacock Premium with my Xfinity subscription. Even though the reward is claimed, the linked Peacock account just prompts me to buy a new plan. When I go to https://customer.xfinity.com/activate-peacock with my Xfinity account, it tells me I'm not eligible. Am I missing something, or should I have access to the Peacock benefit?