Well, a long time ago EU.taralej posted an announcement where he stated that anyone who gets unbanned illegally, that is, without posting an official unban request, is to be rebanned for twice the duration.
However, I wouldn't consider using a rename card to count as an illegal unban. It is true that many players use rename cards as means of escaping bans, but we can't deny anyone the right to use a rename card.
Penalty reduced to 16 days. Consider that extra 3/4 day as compensation for the trouble.