As described this sounds like the classic problem with the DPM around the front door and drainage, especially iof the outside render has blown as described
The other thing to check is to make sure that the water is not coming in from the top terrace area and collecting in the wall cavity, causing the damp so you have to make sure to repair the terrace, oftern where the grounting and DPM fails around the edge of the terrace
The problem with the community insurance is that they will cover the repairs to the astetics, fix the plaster inside and repaint, but not do anything about the source of the problem
If it is a building defect then the claim, depending if the property is less than 10 years old, is on the 10 years NHBC type policy in Spain and the Adminsitrator can give you the details of the insurance company that is providing the cover
You may need to first commission an architects report but normally they will come and inspect the damage
Forget the developer as they will just pass you to the building insurance scheme
If you have your own buildings insurance you could also claim on this which is nornally much easier
I hope this helps but if you would like me to have a look when I am next on RODA please mail me