I went to multiple branches of Bangkok bank today, but they all refused to open a bank account with my DTV visa, does anyone know any branch where I can open an account?

Also on my entry stamp with  they put a date for six months only, I thought this visa was for five years. I got it directly from the consulate without using an agent so I’m completely unaware. How long can I stay in the country and I how often do I have to leave the country and is it mandatory to purchase health insurance? I’m sorry it’s a lot of questions, but any assistant will be greatly appreciated.