You apparently in the 2 months before you apply for a extension of stay period. Best not to change banks now.
You should not need to show a bank statement since you are now on the 90 day stay from the non-o visa. If anything you would on need a 3 month bank statement that be obtained while you wait at the bank when get the letter confirming your account.
You could change banks 3 months after you apply for the extension.