Verison FiOS is Horrible

I disconnected my service 12-12-07. They withdrew money from my bank account in January instead of reimbursing me the rest of December. Now they have sent me to collections for the amount they owe me! I don't know how to get this straightened out. I have literally spent over 100 hours on the phone with them over the past 9 months trying to get this straightened out. What do I do?