I am having the same problem - I pay an annual subscription for Creative Cloud and purchased a single image on 23 February 2018 - after you stopped enabling one image downloads?:
When I went to purchase one today my account has expired:
Can you explain how the February purchase was possible and does this mean I am no longer able to download single images? Like many, many others on this and other threads I simply don't need to purchase large amounts of standard images. Is there any way you can listen to your customers and revert back to single purchase? I think you will lose a lot of regular custom otherwise.
Branching to a new discussion,
I apologize for the troubles that you've faced on the Stock website.
I checked your account and see the single image purchase but that option was available to few of our customer because of their single purchase history with Stock.
Starting last week itself, we have discontinued the single image purchase options altogether.
You can definitely check our credit pack options here: Adobe Stock pricing and membership plan | Adobe Stock
You may also refer to Adobe Stock pricing and membership plan | Adobe Stock for more information on credit packs.
Feel free to update this thread in case of any additional questions.