If your property is under warranty, just write in to them officially that you are going to employ a plumber of your own and backcharge is all to them.

Also, take all the photos you have on the incident day and make a claim to all your damaged goods (due to their poor workmanship).

Consult a lawyer and see if you are able to sue them in any grounds.

If all else fail, gather all the pictures, statement and politicians and hold a BIG press conference nearby their office or at their show units or anywhere you may gather a strong interest (property fair/hotels/mega shopping centres) and disclose it all (warn the developer you are willing to go to this extend if they fail to address you appropriately).

Write in to all major newspapers/social networking sites/internet newspaper and make a big fuss. Create a anti-(insert developer's name) site on facebook and make it viral.

Lastly, file a claim under the consumer tribunal, write in to consumer assicoations, and government ministry in charge of this (is your property under commercial or residential title?).

Sorry to hear about your problems. Hope they solve it for you soon.