I have just done my instructors exam and as part of the test the examiner talks to you about practical aspects of instructing. One of the points he brought up was changing instructors. His point was that the relationship with your instructor is very important to progression on the course. If there is any personality conflict with an instructor changing is very appropriate. Additionally if a student is struggling and the CFI thinks there is a problem if he is good he should even suggest it.
I am hoping to start instructing next week. And yes I am doing it to build hours. However I used to be a student and it really p****d me off when an instructor blatently hasn't got time for you so I know how you feel. Just because one is hour building doesn't mean that you can't be helpfull too. I intend to help as much as I can!
My advice - Don't waste your money on someone who isn't earning it! Change.