I wasn't sure really what to put this under but, we have the issue that our subscription is under the old nest account and we migrated to the new Google when we added new devices. For a little bit we ended up with 2 subscriptions and we canceled one which was on the new items but the old ones are still under a subscription that I am unable to cancel and have it all under one. Any help is welcome.
I'm just another Google Nest customer, and can't tell what your specifics are or why you are unable to cancel one of your subscriptions.
This Google Nest Help topic has information on subscription specifics:
You might want to use the "Contact us" link under "Nest Aware Premier Care" on the page below to "Get 24/7 access to Nest Aware Experts on the Nest Customer Care team. They’re available to answer questions, help you access features, and manage your subscription."