When did you take the plan? It may take several hours up to 3 days before you can manage the plan.
Sorry to hear that you are facing issues while cancelling your subscription.
I have checked your account details and noticed that you had signed up for Adobe Stock-40 images per month(one-year) plan on 18 Mar 2019. The subscription has already been cancelled.
Feel free to update this thread in case of any additional questions.
I need to cancel my plan, today is the last day of the free subscription period, please help me!!