This is a uniquely Bangkok Bank problem. They're the only ones who require this 5 days. They have to request and receive the statement from the headquarters for some reason.
The first thing is that you need to make sure you meet the basic requirements for your extension. That means you met last year's requirements. Your 12 month bank statement will have to show that you kept your balance at 800,000 for 3 months after you received the extension, and then never let it drop below 400,000. If you can't show that, you're already done. Nothing else matters, you won't get a new extension.
If you did meet that, and now you've brought your balance back up from 400k to 800k before you will be applying for this extension, then you're going to have sign a document for Bangkok Bank. That letter gives them permission to freeze your 800,000 for 4 months. Once you sign that letter, they will give you the proof you need for immigration. If you don't sign the letter, you don't get the proof. It shouldn't matter much since you already have to keep the money in your account for 3 months after your extension, so the bank will now just be requiring you to keep it an extra month after that.
Most reports I've heard said that they are requiring you to be married to Thai or have work permit.
You just need to check more bank branches. Each office manager sets the policies for that branch. You just keep checking until you find one that works. But I would avoid Bangkok Bank
There are reports that some embassies have accepted it, but most will not because it's not on the list of soft power activities originally released by the MFA.
no, it doesn't work. The US embassy does not offer income certification which means the only option for the first 1-year extension is 800,000 in a Thai bank account.