First thing I'd do is dispute the $20 fee with my cc company. If you didn't give them authorization to make the charge they've violated their agreement.
You can do a search at
www.uspto.gov for the trademark info.
If that domain is parked (empty/nonsense page) you should get something on it quick.
If you really want to keep the domain, or if you want to try to negotiate a settlement price, you really should consult a domain name attorney as previously suggested. Like someone else said, just by offering to sell you can set yourself up for failure.