I'm surprised the contract didn't obligate you to return most or all of the advance after canceling.
I don't think he ever got the first half of the advance...cherry-picking from the TFA:
> They offered a $5000 advance with the first half paid out when they approve of the first third of the book and the second half when they accept the final manuscript for publication.
> I continued to get further behind on delivering my revised draft of the first 1/3.
> Around this time, there was a possibility of me changing jobs. Oh, and my wedding was coming up. That was the final nail in the coffin.
> There were too many things going on and I didn't enjoy working on the book anymore, so what is the point? I made up my mind to ask to freeze the project.
> They agreed.
The first half of the advance was to be paid after the first third was approved.
They never got to that point.