Notarization of a signature of "Declaration of Work Experience" by Legalization Division of Ministry of Foreign Affairs of Thailand

I am a minority here, I like to leave Thailand... I got a job offer in South America.

Therefore I need to apply for a work permit in that country.

For that I need to have legalized a Declaration of Work Experience by my current employer - an international private school.

The consular department of the embassy of the South American country insists that I have to notarize the above mentioned document by some officer from the Ministry of Foreign Affairs of Thailand, otherwise they can not legalize the document.

Any experiences? How to proceed? For the moment, my employer can not help me.

I have not been to the MFA yet, because I doubt that they notarize a document from a private school.

I appreciate every advise.