You knew you had a balance with them, why didn't you just pay something towards it, with or without the bill ir call them when you did not receive one.

I maintain all my monthly bills on a spreadsheet and just change the figures based on the bill amount. This way, if I don't get a bill for some reason, I either make a payment or call the company for an amount. It's saved me a bunch of times when I either didn't get or lost a paper bill.