If he has done a bit extra than was required I would expect you would have to pay him for the work done. Perhaps you should try and reach a compromise.
I got work done by my solicitor last year and was quoted for the work beforehand. Before job was completed I asked how much the bill stood at, and it had almost doubled due to unforseen work involved (first time this particular job had been undertaken by them and case was a bit unusual, so hard to tell exactly length of time and outlay involved). Nevertheless, I said that I would find it very hard to come up with the extra money, though I appreciate the work involved, as I had only been quoted x amount and didn't expect to pay quite so much more. They reviewed it again and came down a few hundred, because they said they had quoted me a smaller amount in the first place. It was still more than they had quoted but still a lot less than the final bill. I was happy enough with that.
I think if you go back to them as I did, perhaps they may come down a bit on the price.