I Have the same problem. Adobe offer me 10 free images from adobe stock - I use this option. During this, there is a big information than they don't take any money from me...and what happen? Of course after month they open me a yearly subsription plan and take money from my account without my permission!
Because of such non-ethical practices, I will never use their pictures stock!
Sorry to hear that you are facing issues while cancelling your Adobe Stock subscription.
I have checked your account details and noticed that you have signed up for Adobe Stock 10 images per month(one-year) plan on 27 Nov 2018. The subscription has been suspended due to payment issues and that is the reason you are unable to self-cancel your subscription.
Please check your private message for more details.