[tapiwa]

Document the vulnerability. Document your attempts to contact the bank.

Contact your local[1] newspaper. Particularly one that is big on investigative journalism, and technology.

A good hint is if they covered the recent SWIFT bank heists.

[1]Local is relative. If it is a big national bank, go national.

The idea is for them to do an article, not necessarily exposing the vulnerability, but how processes (or lack thereof) in the big banks allow security holes to go unfixed.