What happens if I upgrade, downgrade, or cancel in the middle of a billing cycle?
If you upgrade, you'll be charged a prorated amount for the additional messages in the new plan. These messages are only good for the current billing cycle. You'll then be billed and credited for that plan during the next billing cycle.
If you downgrade you'll be charged the new rate for your new plan starting on your next billing cycle.
If you cancel you'll be cancelled immediately and you won't be charged again, and your credits will expire on the first day of what would be your new billing cycle had you continued your plan.