David , sorry to hear about your problem.
I think you should think very carefully about paying yet more money to action a case against your first lawyer. The cynic in me says, and from a similar experience, that it would be very hard to sue this lawyer for negligence. It’s a common problem for hundreds and hundreds of people caught up in the Spanish property scandals. It appears to be a closed network. I think the only person that would make any money would be your lawyer from his fees, presuming he is willing to represent you should you decide to go ahead.
This is just my personal opinion. I’m sure others will have views on this .