I cancelled my subscription, but invoice says "past due"

I cancelled my subscription the day before the payment was due, because I am eligible for student pricing, and I didn’t know you would keep your benefits until the next billing date.
But it says that my subscription will renew NEXT year, and that I have a past-due payment.
I am concerned that when the billing account has enough money, it will withdraw the money. Is this something I should be concerned about? How do I fix this?