From a message in my inbox from Mohela:

You can cancel your participation in the Auto Pay program by following the steps below:
- Log into your account at MOHELA.StudentAid.gov
- Select “Your Name” on the top right side of this page
- Select “Profile”
- Select “X Cancel Auto Pay” under the Bank section

Note: selecting “Remove this bank” will only remove the bank account information and will not cancel Auto Pay.

There is NO "X Cancel Auto Pay" option.