kingswood property agent very very disappointed

I think you have bought first-hand property because only in that case promise of rebate will be arranged.
All promises from the agent at the time of buying should be strictly made in writing instead of just verbally.
In common practice, the rebate from the property agent will only be settled after the property agent has received the relevant commission being payable by the developer concerned. The developer will usually pay the commission after the transaction has been completed , the property has been completed for occupation and the buyer has taken over the property.
Therefore, in your case, you may check if the commission has actually settled by the developer to the property agent. If yes and the property agent still refuse to settle the rebate, you may complain to the EAA and they will handle your case.
REMEMBER ALWAYS THAT ALL PROMISES MUST BE MADE IN WRITING.

Yes ,It's very be careful to choice agent