That is stupid! I don't even have checks....lol.
I paid a doctor visit online once, and got a past due bill for it later. Luckily, I held on to my confirmation number and had to call. Told them I paid it the day I got the bill and it was over a month ago. She was like, "oh I see your payment, they just didn't apply it to your account yet." WTF? So they slacked on applying it, yet had no qualms about sending me a past due bill. Maybe they thought I would be stupid enough to pay it again.