We purchased a property and the sellers have not disclosed on the TA6 form the water supply pipe is private

The property sellers stated on the TA6 Form that the water was a mains supply and that the stop cock was in the kitchen and on the road which it is outside the property gate BUT they neglected to disclose that the pipe also runs from the property boundary stop cock down 500 meters of a single public country lane to another stop cock which is also ours then connection to the mains. They have also not told us that the pipe is shared with a cantankerous old farmer with no agreements in place. The pipe was leaking and had to be replaced at a cost of £20,000. I have contacted the sellers nicely by letter several times and we have since spent £2580 to a solicitor who has written to them and there solicitor has not responded to our last letter.

We can no longer afford to use a solicitor and would like to take them to a small claims court to pay for half the pipe but are unsure how to go about it as we can't find any reference to this problem with TA6 forms anywhere. We want them to be sued for this as they have lied on this legal document. Can you please advise as we are at our wits end?