Ago I negoiated with them and authorized them to deduct from my checking account a certain amount. For some reason after about 4 months this stopped. Not because of me, but on their part. What do I do?

Please provide a little more info. Was this ia judgment issued by a court or a collection agrrement with an agency? If there was a judgment issued against you, they would not have to make an agreement with you to bedit your account, they could forward the judgment to your back and ask they they levy your account. Please clarify exactly what happened.