wrong debit amount

Homechoice took a debit order early in December which was under debited now my account is in arrears and now its my problem . I can't place any new orders till the account is up to date, I don't see why I would need to make a payment arrangement as I was not at fault . customer service isn't any help ,I keep getting told that there wasn't enough funds in the account to debit the full amount which is a load of bull. I'm really not impressed with the way they are handling the situation