I would contact Cosumer Affairs and see if theres a cut-off date for billing. Once that has been established, you then need to contact your costumer and explain to them the situation. Then recontact your supplier and tell them payment will be forthcoming once your customer has settled thier revised bill. They'll probaly refuse which is fine but it just gives you a record that you have gone to some lenths to recover "their mistake". If they preceed with the Dept Recovery agency option then you now have adeqite grounds to take the supplier to small claims court. You should have a resonable case.
Once youve filed the court order, Contact the dept agency and let them know that the disputed dept is before the courts. They are legaly bound and cannot affect tour credit rating. Ask for a letter of affimation.
PS Find out the name of your suppliers CEO and General Manager and file the order in their name. Then they are obliged to attend. Chance are that it wont get that far however.
