Technically speaking, once OTP is issued and exercised, there is
no turning back.
Cos the OTP is a legally binding contract. Once breached by
either party, the other party has the right to pursue.
Unless seller has a strong case, then is worthwhile to take this
risk. For example, seller is able to prove that they are being
misled by their agent into signing the OTP.
In this case, I think there are no alternatives
already.
And obviously your agent didn't have your interest at heart. He
is more concern with his commission. You should name and shame
him.