Keith you have to hire a -hopefully- good lawyer and sue the developer.
Your new lawyer will advise you what to do in the case of your previous lawyers. I wouldn’t sue them first, take the complaint to Alicante’s ICA.
Guest: you are not coerced, compelled or forced in any way to complete on the new propertyif the developer failed to obtain the building licence.
Pull out, recover all your moneis plus 6% interest under Law 57/68. Consult a lawyer. Don’t let the developer dubb you in to complete an unwanted property if it is not the one from the original contract.