thank you very much for your answers, you are right and I did try explain them this however they knew "better", so that I could not process cancellation with them. Thanks again :)
I just showed my passport in Vietnam embassy and ask about cancellation, they said I can go straight to passport control to get the 30 days tourist stamp and no need to cancel my visa extention because it is only single entry. All seems to be simple but complicated
, so to summarise : I just fly back to Bangkok and go immigration with my cancelling letter from the school to cancel extention then go to passport gate and get the 30 days tourist entry visa?
the immigration at the Bangkok airport? The only thing I can do is to ask school to email me letter today while I'm in Vietnam. Then I can print it out, is this OK then?
thanks for a quick reply. Can I cancel my edu extension on the Bangkok airport? I will arrive 22.30, also not sure if this department operates that time.