When you say the company who built the estate went bust, was it before or after the site was finished? Did home bond or another builder step in to finish it?
When you say the property is unregistered, how do you know? Have you had legal advice? Have you done searches? Is it registered in the Registry of Deeds?
What has this new construction company done exactly- your sentence is hard to follow- please expand on this point.
Does this estate comprise of houses only or apartments or 'duplexes' too? How are the common areas maintained currently?