If your house is newly built then I think that the most likely cause of your
problem is soil compaction.
It is very common on new sites, esp. where the builders have had a lot of
machinery running back and fore over the same ground.
If you are part of a development and are towards the outside of the site
then you may have had the machines running back and for over your ground as
they built a lot of the other houses.
At the end what do the builders do?
They level with the bucket of a JCB and then dump a few inches of top soil
on top , level (Again often with the JCB) then get turf laid over the lot.
If the landscaper you spoke to says it can be rectified then I very much
doubt if you are on a flood plain..
if you can get a long iron bar then try to punch a hole into the ground and
see just how hard it is and at what depth, alternatively you could try just
with a fork or spade.
Try in several places, and I doubt if you will get it in more than a few
inches before you hit hard soil.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk