OP, don't get worked up unless it is your first payment due on the first loan you ever had.
They may report it, but if you've had several on time payments, one won't matter much.
People make mistakes, mail gets lost, mail comes late.
BUT: you should now know what payment is due when, and roughly when it should arrive in the mail, so next time it gets to a week before the due date, give them a call and let them know you have not received a bill.
See also, if you can, to make payments by phone if it comes close to due date.
You can also ask for them to change your due date to an easy to remember date, like the first of the month. That way when the 25th arrives and you haven't had a bill, you know to call and make your payment. To do this you might need to make an interim half payment or make a larger payment the next payment.
Don't stress over it though.