There is a hotline in greek language, provided by the german pension insurance in Baden-Württemberg (that ist the connecting institution to Greek):
0049 711 848 15111 or 0049 711 848 15113
You can also check the information online:
http://www.deutsche-rentenversicherung.de/BadenWuerttemberg/de/Navigation/0_Home/home_node.html
In this case you have to change to "Eλληνικά" in the upper menu "Fremdsprachen".
Or send the document to:
Deutsche Rentenversicherung Baden-Württemberg
Standort Karlsruhe
76122 Karlsruhe
Germany