Ok so a client of mine had an employee setup their original website through vistaprint. They ordered a VPS through me and I designed a new website for it on one of my other domains.. the employee who set up the original account is no longer with their company and will not give us the login information.
Vistaprint appears to register their domains through tucows. I have contacted vistaprint and tucows to try and get the information but neither have answered their phones or responded to my emails.
The owner paid on his credit card from what I was told so by all means it should belong to him.
You should always register a domain name under your own name. That way you have control of it. Since the whois details are vistaprint, it really means that they own the domain name. So, there's actually not much you can do.