It looks like you have a month-by-month subscription, and you can cancel anytime without fee (self cancel: Cancel your Adobe Stock membership). The 3-assets-per-month is an old subscription offer that is no more used today, so I cannot check the conditions, but generally subscriptions allow to accumulate a year of assets (so that would be up to 36 assets in your case). If you have licensed assets, they will stay with you when you cancel. The unused asset points will be forfeit at the end of the subscription.
You can check the current status of your assets here: https://stock.adobe.com
Abambo is correct you can cancel your 3 asset plan anytime as it is a Month-to-Month subscription. This plan is still offered but not in all locations.