Hi Steven, You certainly have a right to be angry...at yourself! To have a business that might deal with English speaking peeps, and yet NOT buy the ".com" when you were buying the ".es", reeks of a shortsightedness and/or an incredible cheapness, as a URL goes for around $7 per/year.
Having said that (and harshly), I do understand your basic problem: they want to be connected with you, but you don't wish the reverse. Because they are using your good name to gain type-in traffic through a parked domain (ie no constructed website) you might have good cause to appeal their ownership....but it still might need some funds to change hands. Of course you could buy every variable of their URL, and point all to your site...but unfortunately most peeps type in ".com". Plus you want distance from them.
Personally I would work on your "brand". Both Google and Yahoo have various tools by which you can find the most popular searches performed over whatever period of time. Type into these tools search terms with which you think peeps are using to find you. So..."spanish property lawyer" might have been searched for 1000 times last month. So buy a URL with those words in it! Make a blog out of it. Cover it in lots of pretty banners pointing to your REAL site. Optimise the site for search engines with keywords, tags etc. Rinse and Repeat. Link all together. And within a short time you'll have a nice traffic network. Once peeps hit your site, make sure you encourage them to bookmark/add to favourites. And most important of all, don't get mad....get even!
PS Thankyou for the great job you do on this site. People like you really do make a difference. You have calmed many a nerve!
PPS I understand that Justin is doing SEO work...so I'll not tread on his tippy toes any more. Whenever I read of him here, he's either shopping, crashing his car, eating or motor racing. So I'm sure he could do with a real job!