Before I wrote this post I had been chasing him for two weeks to come and finish the job. He only got back to me yesterday, so I'm guessing that his livlihood doesn't depend too much on this job.
I contacted him again today and asked him to finish the job to our satisfaction so we could settle the bill. He declined and advised us to use the money owed to get someone in to fix it. He knows that he's messed this up.
There are certain standards that are expected in any job, to say that he's done what was asked and deserves to be paid is ridiculous. If a painter and decorator painted your house and left big streaks all over you would expect it to be rectified before you paid them.
You didn't state in your op that you had been chasing him for a few weeks or that he had said he was happy to let you get someone else in.
If you've given him fair chance to rectify and he hasn't bothered then you are right to seek help from elsewhere.
We can only comment on what you write.