If you cancel a Month-To-Month plan in the middle of a month of usage, your bill for that month will be prorated based on how much of the month you used.
If you signed up on June 15 and cancel 5 days later on June 20, you will be billed for 5 days only:
5 days used / 30 days in the month = 1/6
Therefore, you will be charged for 1/6 of the monthly cost, based on your peak usage during those 5 days.
If you cancel on the same day as you sign up, you we not be billed anything.
To cancel your Month-To-Month plan:
Open the Manage Account page.
Select Administration from the top menu.
Select Manage Account from the side menu.
Select Change your Plan.
Select the Cancel your Plan link.