WOW........ what a horrible thing to have happen to this guy!!!

This guy MUST get an attorney and go to the base of the problem---the fact that he was denied the opportunity to appear on his own behalf. That has to be addressed fully...........I do understand that addressing that takes time and in the mean while, I think you are right on the money (pun intended) by expecting the court to recognize the court order, even if it isn't a 'GARNISHMENT ORDER FROM CHILD FAMILY SERVICE'.

Also of concern to me is the fact that while he was unable to keep to the terms of the original credit card agreement, he DID make other payment arrangements to keep the matter out of court according to what you have said---but they went ahead and took him to court while he was in keeping with the subsequent agreement. This is not appropriate, since the subsequent agreement supercedes the first. It is my feeling he has a strong leg to stand on in court regarding the actions of this creditor.
In sad situations like this, the "big guys" get away with what they can and it is a downward spiral until an attorney gets involved and stops this flow of errors that are happening one upon the other. Your client is fortunate to have you in their corner.