Have you spoken to your agent's boss, the BROKER?
I would call him/her and explain why you're unhappy with the agent. See what he/she offers to do.
I would also call a real estate attorney if you are not happy with the Broker's response.
I am the broker of my company. I can tell you that if someone calls to complain that they're not happy with someone in my office, or our services, I would never force them to sign something they were unhappy with. I also would never personally pursue a commission (even if we bought full price offers to you) if there was a good reason to reject them.
Situations change during a listing. If your situation has changed and you want out of the listing contract, tell your broker the truth and see what he/she will do for you.
Personally, I believe a satisfied client isbetter than an unhappy one who will spread bad press about me.