Cannot activate Peacock upgrade

I already have an activated Peacock Premium subscription which Xfinity gave me for free. Recently I decided to upgrade to Peacock Premium Plus, and my subscription page says it needs to be activated. But when I try to activate it on the Peacock website, it says that they cannot activate it because my email address is linked to another Peacock account. I assume this refers to the Peacock Premium subscription that I already have. But I cannot find a way to cancel that subscription to activate the Premium Plus subscription.