Consumer Law, Warranties Contract Breach

[Chrisddhd]

I had a proposal from a contractor for excavation work on vacant land, we had a written proposal and verbal contractual terms. He is not in compliance with the written proposal or verbal and I have him on audio tape agreeing that we had a verbal contract and the terms that we agreed upon but he claims" even if he agreed to it he does not have to honer it because it ain't in writing". He did half the job and wants more money after I paid him half. Can I fire him and how do i do it, I'm sure I'll win in court, he not too swift but i want to fire him and limit any future liability. There is nothing written or verbal about how to cancel the contract. What should I do, sue him or let him take the first step?