At this point, speaking with an attorney might not be a bad idea, especially if PayPal takes further action on that negative balance, but there are a few other things you can try first.
Customer service is going to be useless, but you can try contacting the executive office. I can't post the email address here or it will be removed, but you can deduce it - put the name of the department in front of the PayPal domain, and that's the address.
You should also immediately file complaints with the Better Business Bureau and the Consumer Financial Protection Bureau. Public pressure is about the only thing that moves PayPal to do anything, and while I doubt it will do much in this case, it's worth a shot.
