No option Download the stock images for the paid credits

In addition, to what @Jill_C says, credits expire after one year. You should look at it differently: you do not pay for credits, but to be able to licence assets at a certain price. With that subscription, you get each month an allocation of X (standard) asset credits for up to one-year credits. Basically, you are paying for the ability to access the site and to licence assets. Adobe, in the meanwhile, invests a lot of money to add new assets to the database and to keep the infrastructure up and running. That costs a lot of money if you licence assets or not.

Read your Adobe Stock Agreement. Unused credits are forfeited at the end of the subscription period. This is also clearly stated on the page which describes how to cancel:
Cancel your Adobe Stock membership
Caution:  By canceling your Adobe Stock subscription, you lose access to any unused licenses.

If you haven't cancelled the subscription yet, you can go back into your account and license/download assets to use up all those credits. You should also download all previously licensed assets so that you have a copy on your hard drive, since your Library in Adobe Stock will no longer be accessible after cancellation.