I would echo Whilrygigs advice, go have a word and express your concerns over Instructor avaliability - ask them why you keep getting dumped by them? Is there a legit reason or have they just not turned in or moved you round?
Unless you are really really not happy I wouldnt leave the school just yet, if you are happy with them apart from what you have stated then I would give them a chance to rectify things. As someone else there are a lot of over subscribe schools and you may find that by moving you end up in an even worse position! You have only to read some of the threads on here about whats going on at various schools to see that if you find a good Flight School (just like a good builder/plumber/leccy), hang onto them!!!!!!
J.