In order to unlock your old iPhone 6, you would need to contact customer service. Alternatively, you might consider sending @FidoSolutions a PM. Once they verify some information, they will also be able to access your account. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Have you verified that phone is compatible with the local networks at your travel destination?
Hope this helps 😀