The Thai Consulate General in Munich confirm that I can extent my O-Visa under the terms and with the documents as stated on the homepage of the Thai Immigration under visa extension point 22.
The Immigration in Koh Samui, however, told me that single entry O-Visa can not be extended. I am not the only one here in Koh Samui who have the same problem-
Maybe Obonjoe or somebody else can give me and all the others some real information