Phone Unlock

I recently lost my XR so had to revert back to an old 6S. However I've just broken that now aswell, so will have to use another 6S that is locked. All I want to do is keep the same Vodafone contract that I had on the other 6S and use it on this one, however it is locked. Is it locked to Vodafone or the other provider EE, and who do I use to unlock it?

Thanks