selling a business - should agent do this??

[catkin14]

A business that I own has been for sale with an agent. An offer was received which I was not overly happy with but agent pressed to accept.
Offer was verbally accepted but it is still very early days. Agent said business would stay on market until papers signed. And if a better offer came in, that would be accepted.
Some new prospective buyers approached agent for details, only to be told no further interest would be taken by agent as an offer had been received and accepted.
This is not what I was told by him and new prospective buyers could be offering a better price.
Agent is on a fixed fee contract so it doesnt matter to him what price is actually achieved.
I have emailed him asking what is going on here but what to do next?
Can this sort of behaviour on his part cancel out the written contract with the agent? I certainly do not trust him anymore!