Recurring donations can be stopped from within the platform.
Navigate to your Contributions List.
Select the radio button for "Recurring valid" to view only recurring donations during a specific time frame (i.e. remember to set the date picker to your desired time frame).
Click the green plus sign icon to the left of the donor's name.
Scroll down and click 'Cancel Recurrence' in order to stop the the recurring contribution.
Once confirmed, the donation will no longer repeat it itself on a recurring basis.
If the "Cancel Recurrence" button is dimmed, then the recurring donation is no longer valid/recurring.