A debt.

To have got to this stage where a justice of the peace has allowed siezure of your goods means that you have seen and ignored many multiple reminders, sumons, last notices etc. over an extended period of time of months. You're not in a good situation and you should have acted far, far sooner. Your only course of action now is to contact the CPAS at your local commune. They deal with this sort of thing all the time. They may be able to help you delay proceedings, and negotiate a payment plan.

To answer your specific question, the answer is yes, absolutely they can do that without you being there. The only thing they need to do is present proof of a valid debt that hasn't been paid.