@CarloD
For our Nest Aware Plus subscription (since 2020) we get an email confirming the amount charged for our annual subscription, with the tax and total amount, specific subscription, and payment methods.
If we go to the Subscriptions Management page (https://store.google.com/subscriptions), select the subscription, and select "View payment history" we get a list of recent transactions, and we can select "View transactions" to get a "Completed purchases" page.
If you're still on a 1st gen Nest Aware subscription, I think you should be able to check your subscription here, but I don't know what level of detail you get:
https://store.nest.com/account/subscriptions
