A plumbing company did terrible work installing a main water line. I want it fixed. They won’t accept partial payment. What’s next?
What constitutes "terible work"? From your question it could be anything from the water company refuses to install a meter, to the grass seed in your lawn didn't take.
First, document your issues. Send a letter to the contractor outlining the problems. Take photographs of the areas, and keep a daily notebook of difficulties that the defects have caused and any associated cost (ie: (date) cancelled lesson due to arena footing , or (date) farrier unable to get truck to the barn, etc). Be as specific as possible.
Second, contact two contractors to get costs for correcting the issues with specific line items for each.
Third, be prepared to pay to correct the items and/or respond to a lien claim for the outstanding balance.
As always, contact an attorney in your jurisdiction.