Groundwater coming up through my kitchen floor - help!

Medhuil

First post as it's been recommended I post here for advice - be gentle with me please...
Before Christmas we started to have hefty quantities of water coming in through the quarry tiles in my kitchen (40litres plus). Kitchen is slightly below ground level, 200 year old end terrace with granite/cob wall construction so like many of these old houses, built pretty much straight onto the soil. After a month of poking the water board, they come out, hold up their hands in horror, put in 10m of new lining and three new manhole liners. They fill a manhole with water and put dye down and it piddles up through my kitchen floor, we all agree, that's their dye, this is my kitchen, it's coming up through my floor. "That should sort it!" they chuckle.
Except it hasn't, has it?

The water board have reached the limit of their involvement, they've repaired their installation and the "voids" they've identified under the house where groundwater is now able to come in (in the same places as their drainage water was coming in previous, I might add) are not their problem. They won't investigate the voids.

The ongoing insurance claim is to put it back to its pre-loss condition, not to investigate the cause. The case has gone to the water board senior management team for resolution, and we've been told that we've been recommended for compensation and that because the dye test clearly came up through the kitchen floor it seems "black and white" (their words) that they were liable.

Previous to December we had no problems at all with water coming in. The civil engineers who came out to inspect on Christmas Eve reckoned the deterioration of the water board installations (which are neither on, nor serving, our property, but back onto it) has probably been ongoing for some time until it reached the point where it had washed out channels through the soil, and here we are. 

Where do we even begin to assess what damage has been caused, and how do we get it put right?