I'm sorry that you didn't notice, but the terms and conditions of a stock subscription clearly state that when you cancel, you lose all accumulated and unused subscription credits. Any assets licensed, can be still accessed, given that they did not have been deleted from the database.
From the Terms of Use:

14. Effect of Termination.
(A) If your subscription ends, or upon termination of these Additional Terms, then:
(1) you will forfeit all rights, title and interest in and to any and all unused credits or unused standard assets from a subscription plan, as applicable;
It is also documented in the cancellation help documents: https://helpx.adobe.com/stock/kb/cancel-membership-subscription-stock.html (emphasis by Adobe):

When you click cancel, you get notified that you will use all your unused licences.
You can claim that you didn't know that, but you cannot claim that it is not documented.