Well after getting angry with the Developer for "alledgedly" not telling us there was fill (when there wasn't) we then contacted the people who did the soil test directly - explaining to them that there can't possibly be any fill on the block and I gave them compaction reports for the blocks around me that DID have fill. Our block didn't have fill - therefore didn't have a compaction certificate.
They agreed to retest the soil and like magic our soil test didn't just not require piering any more - it actually came back as a S-Class Slab!! We just saved ourselves $4k! :D
It got us thinking that if we never kicked up a stink in the first place, the builder would have conned us into spending $20k more on something that was never required in the first place! I guess at least its worked out in the end though.