louloo, as far as I understand you bought a re sale apartment in a good location (I hope since most of the CD apartments were in good location) which has a tenant inside and a promise that someone (the seller) will renovate it for you....
the lawyer that made the contract is the seller lawyer not yours , you don't share him in that aspect, 1st thing to do is to find your own lawyer to inspect the contract. in most contracts the seller can enjoy all the income until transferring of possession, so he take your 30% and also get the rent, which makes it a nice deal from his point of view.
however if the contract specify a date of completion you most probably has a good reason to ask for cancellation of the contract, which also mean that you can make an application to the administrative office and get back the stamp duty which you paid, the only problem is that most probably you will need to go to court to do it.