Your visa wasn't canceled, I think your visa application was canceled. If you say your visa was canceled it sounds like, after granted, it was canceled, what reportedly has also happened.
many banks in many countries allow tourists to open bank accounts, so the "like everywhere in the world" has nothing to do here. For this regard, anyways, only Thai regulations matter.
You don't need to leave every six months. You can stay one day and leave, then come again and stay one month, and leave two months. It's totally free and up to you. Each entry grants 180 days.