I once had a similar deal when I lived in a house with several guys for a year in college. We divvied up the utilities, and I was in charge of the phone bill. I set up automatic payment, and never had a problem. But 5 years later, the phone company accused me of skipping my June payment, and carefully deducting that amount from the "total owed" amount in every subsequent month. It's insane, and every human I spoke to agreed with me, but no one had the power to do anything about it. I could either travel cross country to go to court, with no evidence other than common sense, or just pay the $30 bill plus another $40 in penalties.