Roy,
Take a look at the thread copied below. It has all of the contact details you need for Grupo Lar, including Luis Pereda's email address. I recommend you contact Mr Pereda directly, copying in his colleague Alberto Salamanca. A fax is less direct and easy for people to lose!
http://www.eyeonspain.com/Secure/MsgBrdsPosts.aspx?thread=13895&dev=E710&name=El%20Capricho%20De%20Dona%20Julia
This worked for me and I avoided a costly and time consuming litigation that my lawyers were trying to convince me was the only option left.
I got my money back plus legal interest, despite my contract stating I was entitled to 50% compensation. With the state of the Spanish market as it is and the number of property developers that are facing financial difficulties / bankruptcy, I was just happy to be reunited with my money and with the legal interest and favourable currency rate, managed to make a pretty decent return!
I would say the chances of you getting more than your money plus legal interest are zero, despite what any contract says and despite what lawyers such as Lawyers of Spain might tell you. It is a carrot to encourage you to go for the litigation, but is a red herring in my opinion. I would encourage you to cut your losses and try to get back your money plus legal interest, despite what you (and I) feel should be paid. Holding onto the hope of a payout of the sort of amount you are talking may end up with you getting nothing. If you make a realistic proposal to them, they are more likely to enter into discussions with you.
Happy to answer any questions if it helps you and others get your money back.
Good luck!
Ed.