Mary and all:
My apologies for this late response. Very busy these days
Is there a clause like this one in your bank guarantee?
“solidariamente, a primer requerimiento y con renuncia a los beneficios de previa excusión”.
” jointly and severally, at the first request and waiver of the right of excussion”
That would be direct, but it depends on what your aval says.
You will need to send a legally unquestionable request to the bank, with enough evidence of the failure to comply by the developer.
If money is not back then , you will have to go to Courts in an executive fast procedure.