I've looked into this and finding another lawyer to take a lawyer to court is the problem.
I changed my lawyers, (I can't say publically who they were for fear of litigation but my UK number is 01270 259740), almost 2 years ago, to GM Legal Experts who said they would be prepared to take my last lot to the Murcia Law Socierty but the advice I have is that all they'll get is a rap on the knuckles and a letter of reprimand. I certainly won't get my money back, £22K plus 7 years interest!!!
Litigating against a lawyer in Spain is expensive and you shouldn't judge Spanish Law in the same breath as English Law, and yes you are right their insurance requirements in no way match those of the UK.
It looks like you are in the same position as I am. My deposit was never transferred to the bank issuing the guarantee and although under Spanish law 57/68 this shouldn't matter nevertheless my ex-solicitors signed a waiver preventing me from suing the bank, something I explicitly told them not to do.
You can read more about my plight at www.3molinos.co.uk.
I wish you good luck but I suspect it will be all bad. I'll never set foot in Sapin again, I hate the country, it's lawyers and legal system. Most of all I hate the Spainsh government who should tell the banks to voluntarily comply with 57/68, and I hate the UK government for letting them get away with it. We should kick them out of the EU and tell Santander to get of our high street.
Rant over!