Negative J-coin balances are applied when there is a billing dispute. Such as paying for membership, keys, or runecoins and you're banking establishment demands Jagex reverse the charges after you've already received the goods.
So Jagex puts the account into a negative J-coin status so they get their money plus the fees associated with having to reverse charges. So you'd need to contact the billing support team about this. As we as f-mods can't see your account information.
When the day becomes the night and the sky becomes the sea, when the clock strikes heavy and there’s no time for tea; and in our darkest hour, before my final rhyme, she will come back home to Wonderland and turn back the hands of time.