When was that? In a non-existing peace-treaty, possibly?
It is quite possible to argue that we're still in WWII, as there was no peace treaty between the German Reich (or the FRG, which assumed the administrative rights over most of its territory) and only the troops capitulated. Also there's no peace treaty between Japan and the USSR, there's probably a few more trivia bits that I'm unaware of.
Also, Germany (the population, actually) was supposed to get (give itself) a constitution during the reunification process. This was successfully avoided as well.
As there's no proper lever against Germany (e.g. Germany only submits itself to rulings in Den Haag, for situations that occurred after 2008), theres not a lot Greece can do, except default in their face.
(I'll be happy to provide sources, if you require them, but these facts are pretty much common knowledge and easy to find.)