Ray, that sucks for sure and they should have treated you better.
However (just so you are aware) the ADA applies to employees and only to customers IF they are required to provide a service for them. In other words, if they don't have a public bathroom then ADA does not apply to the public for bathroom access. They are a bank and are not required to provide a bathroom for customers like a restaurant is.
Given that, they should have provided better customer service in a bathroom emergency and provided some accommodation (although not legally required to do so). Your best bet is to make a complaint to the highest levels of the Company and bypass the local branch to be heard. Don't remove your assets yet and use them as leverage by threatening to do so if they don't respond appropriately. Then when/if you do, have the press there to cover the story and record you removing them in protest of poor customer service.
It sucks, but they aren't required to give you bathroom access although common sense and good customer service ethics should have compelled them to do so. Especially in the small town environment in which they are operating where customer goodwill is paramount.