One thing that really sets me off is when humans act like they have no control over what their computer says. Or does.
Talk to the manager. Tell him or her that you want them to explain to you line by line, day by day, transaction by transaction how they arrived at the balance they show. (If it does not match what you think it should be and what someone at the bank told you it should be)
And don't let them try to confuse you with a bunch of bank words. If you don't understand something, tell them.