If this is the case, you have a clear claim founded on an existing hidden charge. You would not be able to undo the contract since the breach is not on an essential part of the contract, but you can claim the money from the developer together with interest and damages, as appropriate. Also, if the vendor knew there was a charge nd did not disclose it, his liabilities could even be criminal.
It is nonetheless surprising the developer was not up to date of these payments in the units which have not yet been sold.
