Carlisle homes site cost -additional $11k- infill after demo

Hi all,
Have been a long time reader - first time posting. Sincerely hoping someone can help my hubby and I.
A little background - we are building with Carlisle homes VIC, our site is a knock down rebuild, demolition has been done a couple of months ago and have been awaiting the hydraulic report. Site is a P class and classified as in floodzone according to Dandenong council. Slab is a Waggle raft slab with screw piles. Have received notification today that there is a 200mm difference between our first survey report pre demolition and second survey post demolition. They have stated that we need to import 150mm of fill to site over entire building platform in order to meet Melbourne water flood level requirements to have the building permit issued at a cost of $11,500. Additional site costs prior to this total approximately $60k on a level block (850sq). The site costs are to the point ($70k+) where we are seriously considering pulling out of the contract. Can anyone suggest how I can challenge this additional cost? To my limited understanding the floor height has to be higher (300mm) above the flood level height. I have asked Carlisle to supply me with the council report stating the flood level and break down of the stated cost for the infill. All I have been supplied are the surveying report and stated costs. Can anyone please guide or assist me regarding the steps I should take, it would be greatly appreciated.
Thanking you,

Your site costs are spinning out of control that is for sure however pulling out of the contract might not be the solution as the next builder is going to face the same challenges. If you're building a double story home that might make a difference on the site costs as you have more weight on a smaller lot as opposed to a single story which is less weight over a larger space.
Not much help sorry but good luck!

Thanking you for the reply, yes it is a double story home.

Macca thats a lot. Do you need a waffle slab? Would an alternative platform be cheaper?

Its a waffle - 610mm with screw piles. I have asked them about an alternative slab - awaiting reply.
Anybody here with experience of infill? 1.5cm for $11.5k seems excessive to me - Carlisle homes will not supply the quote to justify this cost of course.

CH site cost is a rip off, heard from people around doing with them. For a friend of mine gone up by around 20k. My understanding is that they are doing it as a strategy.

Waffle slab is the only slab CH does, not budging on providing me the costing breakdown. Lesson learned.

We have almost $5,000 charge for 75mm of fill with PD.

Thanking you - These volume builders know how to hit thats for sure.

I couldn't believe it, 75mm is nothing!!!