Succesful extension.
Yesterday my husband and i went to Koh Samui immigration office. We had a letter (printed PDF file) from the embassy/consulate of the Netherlands.
We already had 60 days tourist visa and 30 days extension so we asked for an extra extension.
They asked us to come back the next afternoon to pick up the passports.
So today we went, picked up the passports in 5 minutes and got 15 extra days, then we have to come back to immigration to get a stamp for the other 15 days. No questions were asked so it was very easy.
It was extremely busy today though! But we were lucky to already have an appointment to pick up the passports.
Good luck everyone!
TLDR : Answer Summary
The user successfully extended their tourist visa in Koh Samui by providing a letter from the Netherlands embassy along with their existing tourist visa and extension. They received an additional 15 days after a short visit to the immigration office, with no complications during the process.
