HIA CONTRACT QUESTION

Can anyone assist with info – 1st time building IP – We were put onto a builder who had hold on land we wanted and agreed to build through him. At this time we were told the land was registered (should have checked I know) as it turned out it was not but were told by builder (who was on the spot and we were in Sydney)that it would be soon so we signed land and HIA building contracts in July 2004 and paid half the deposit on the building contract at that time. Land did not register until Dec 2004 at which time builder said it was too late to start prior to Xmas and holiday time. The construction commenced Jan 2005.
We believed it to be a fixed price contract (but looks like it isn’t – have learnt my lesson – will have it checked out by lawyer next time!))and house is now completed – we arranged for final payment from the lenders loan amount leaving only the variations we had done to pay for from our own finances.We had only verbal agreements for these costs – nothing signed – bottom line he has sent invoice through for the agreed quoted costs but he has now added 12% margin with 10%GST on top which has added substantially to the total. He rang me prior to faxing this through and during the conversation said that he had inflated it to cover his costs however that he was really entitled to invoice us for double the amount he is asking for as there is a clause in the contract which allows him to do this.He said we could check this with HIA – something to do with delay in having land available for building to start – this delay then meaning he had higher building costs and that he could pass something like 9% of the contract price onto us. He said that he had never done this with previous similar situations and didn’t want to do it now but I think he was effectively waving the “big stick” – pay or else this is what I will do.
When we signed the building contract there was nothing else attached except for the building schedule and attachments detailing prime cost and finishes included.
After phone call rushed home to scour contract and came across “The contract price is subject to change. The clauses that allow for changes to contract price are clauses 9,10,11,13,15,16,19,20,21 and 22.”
We have been naive haven’t we to say the least ? – Can anyone tell me what these clauses mean as we did not receive any contract information statement in Annexure 2 (which is referred to later in the contract)and didn’t sign anything else.
Do we have a out anywhere to avoid paying the 9% on contract price if builder decides to do this ?
Should we just take it as lesson learnt and pay the invoice he has sent ? Can he then later hit us for further payment or do we ask for a signed statement prior to payment stating that it is in full settlement of the contract siigned and dated between us in July 2004 ?
There is just one more complication and that is that we have tenants ready to move in next week and I think that the property managers have made him aware of this..
Any info, insights, advice will be gratefully received…

MIKALA