Did you cancel your plan by mistake, or just want to resume your plan? You have until the end of the billing cycle to resume your plan. Here's how you can resume your plan.
Within the sidebar, click the Settings icon.
Then, click "Billing" on the left navigation. Within the Plan section, click the link, "Cancel Plan".
Click the button, Resume Plan.
You're all set. Your plan will no longer be cancelled and your credit card on file will be charged at the next billing cycle.