After 6 months of wrangling, arguments and legal-ish letters we got them to pay the emergency plumbers fee! I don't have the time or energy to go back into battle for the 'make it right' costs, and our buildings insurance wouldn't be worth claiming against for such a small job...
Their pipe runs through your home and they are being dicks about it leaking!
Get a plumber to cap off the pipe that you don't need. or replace the inline connector that I mentioned before with a shutoff valve until they agree with the repairs.
You probably know this, but somebody's insurers should be dealing with this and paying for it.