well.... SDP have many branch and division,
yes- so key projects like Elimina sure will be prioritized, it get lots of attention and they have many more phases to be sold ( in premium price )

for your case, i would suggest to be present at the after sales office, request to be escalated.
bring the defect letter, and also prepare a complain letter and pass to them. Request them to acknowledge receipt if possible.

record all the dates down and who you are dealing with. A complete log is important, and email them the log when ever any progress/feedback from them, or any additional complain/letter by you.

all this will be helpful in case it need to be escalated/litigated later.
Also i know you are frustrated and piss off that they are not responsible, but do control our manner and temper, do not go until insulting as they are only employee- and have their constrain.

Keep your calm and escalate step at a time.

And yes, per Vinceleo says... you may get own contractor to rectify and deduct from the retention sum. but how easy/hard is the process, - we dont know as yet.

really piss off eh.
when buy time promise sky promise earth promise sea.
we as consumer really need to beware... take a huge discount on the selling points, good feature, nice concepts etc.
make own judgment and don't let emotion over right the decision.