Depends on why you are in negative Jcoins.
When I was hacked, they bought members, and when I recoverd it my account went into negative Jcoins, because they "chargebacked" the membership so to speak. I emailed billing support, and they removed the Jcoins. Other than that, you could perhaps get your parents to use their debit card? And pay them the money? Or else, you could buy a Card from like sainsburys.