Yeah, i'd recommend changing.
Also, look for private instructors (ones who have there own company in which they are the only teacher). This is because they can only survive if they get recommended and therefore tend to be better then those who work in red etc. (who tend to be people who just want a job)
Ask friends and even teachers!
I passed first time after 25 hours of lessons (he said I could book it a few lessons sooner if I wanted - so not a scammer at all!)
My sister had 2 before switching to mine (one from the AA and one from 17+) and failed once before. She said my one was by far the best! So look for independents!
Finally, get as much driving with rents as possible, and ask to do maneuvers and if (s)hes not forcing you into any. I was made to do a bay park in my first lesson!
And dont worry, if you do enough practice you'll breeze though your test, just be patient otherwise your impatience may make you an erratic driver.
Good luck (and i'll give you the name of my guy if you are in the norfolk area) !