I want to go to Mae Sai to extend my visa stay in Thailand bit I’m not sure if the borde is open. Can you tell me?
Yes! Currently (January 2017) you can go to Mae Sai 2 times per year if you only have a 30 Day stamp in your passport. Crossing the border there will allow you to get an additional 30 days. Remember that each entry can then be extended at Chiang Mai Immigration office for an additional 30 days.
If you have a miltiple entry visa you can also go to Mae Sai as before.