I would set-up a new domain and 301 redirect all visitors and then go around updating backlinks to point to new location, ok you will lose some work and create a lot more work that needs to be done but at least its a lesson learnt.
The problem with this is that the domain name would not be his. A big company can argue anything about that email if they wanted. But the truth is, they can revoke that right. You did not pay for it, you do not own it. Maybe it was their plan from the start: let you build a website with visitors and then redirect those visitors to their website. Who knows what they were thinking? The point is that if these guys are as big as you say they are, they will win unless you spend a lot of money on lawyers.
I wouldn't worry about it, There is not much they can do unless you are actually trying to pose as them.
ur chances are not looking good. Trademarked names are one of the most protected digital property... im guessing this has something to do with munnnnnnsterrrr cobles. (deliberately mixed for legal reasons)