Yes, I was specifically told the property could be sub divided/developed - I would not have bought it if it could not be.
You are in a frustrating situation and responsibility for signing contracts would rest with you.
Did you check said advice with council?
Did you check or were you given any comparable sales of similar properties to assist with your due diligence and to establish that the BA knew what they were doing for you or had your best interests in mind?
Was your brief in writing that property must be able to be carved up?
Were you specifically told (verbally) or in writing/email or both?
And......finally, here's the conspiracist in me, bearing in mind the disparity in price/value, were they selling one of their (own or relatives) assets to you?
If you have something in writing that constituted the BA fulfilling their brief and they didn't.....perhaps you may have recourse. My comment is not advice merely trying to think out loud with some logic.
I feel for you and whilst I don't use Buyer's Advocates (I enjoy the hunt myself and like to be in total control), they have a purpose for time poor, non-local or novice investor purchasers. End of the day though, the buck stops with you to check that their leg work and offerings are reasonable in price for what you're getting.