I would write the transition documents as my first priority and then as time allows, work on what I can in the time I have left. I think even if you finish every scrap of work and write fantastic transition documents, this company may not give the glowing review you are seeking (mainly getting that from the phone conversation you had), so please don't knock yourself out. You will be even more upset when you kill yourself doing it all and they still refuse to provide a letter of recommendation.

Also - regarding the phone conversation. In the future if this ever happens to you again, tell the caller they caught you in the middle of something and you'll need to call them back, then consider what to say and return the call. While they seemed to be asking why you were leaving, they didn't really want to know the truth. Be vague, mention needing a change, better opportunity came along, whatever.