Dilemma with water Bill

We have a farm and a complicated water situation.
The main supply of water is at the entrance to the farm - about a mile down the farm track and on the mainroad. There is a stopcock there and a water meter.
Up the track is the farm's private supply, which also goes to several houses and another farm.

Previously the water was supplied by South east water, who billed us monthly and we paid for this.

Last Summer it appears that the water company changed hands, now with Castle water. The new supplier didnt bill us for 3 months, and then sent us a huge bill, quickly rising to a final demand. It seemed quite alot more than usual. The bills had previously been handled by my elderly relative and this was dropped in my lap when the final demands came in. This was in January.

After looking at the bill it was clear that this was an estimated bill, based on a fortnights use in high summer, during the heatwave, when we had summer camping going on and 2 farms worth of thirsty cows which now we no longer out to grass. Furthermore this estaimate came from Southeast water, who allegedly read the meter on 15th June and again on 30th June just before the transfer took place on 1st July.

This is where it gets interesting. We spoke to castle water who highlighted a problem with the main supply meter. They commented that they had done a meter reading and that it appears that the meter had 'rolled back'. We thought this sounded a bit suspect, so we went and read the meter. The meter reading was exactly the same as the 'actual reading' taken by South East water on 15th June. I remember that earlier in the summer there had been an incident where water was pouring out into the street on their side of our meter, and they had come to fix it, so it has made me wonder whether they damaged the meter at this point.

This also suggests that SouthEast water falsified the 'actual reading' taken on 30th June to try to avoid the responsibility of fixing a broken meter for a supply they were handing over to a third party.

Back in January we provided this to Castle Water and sent them a time dated photograph of the meter still with the June 15th reading.

They told us they would sort it out and that the account would be put on hold while they did this.

They have now sent further estimated bills (based on SE waters 'faked' figures) although we have managed to track down the guy in customer service who has again put the account on hold for a fortnight to supposedly let them contact SE water to see whats going on.

Any advice as to what we should do? I am hesitant to pay estimates that are potentially based on figures gained during a period of high use. There is no evidence whatsoever of how much water is being used.