This is strange:
FIRST - the sale contract has no exit clause. That's a major flaw. I believe it can be contested by either party as null and void. Usually, sale contracts provide for a 10% (of the contract sum) penalty for inability to conclude the deal.
SECOND - If you are buying the house, why should you be paying rent on it? Think about it, if there was no documentation problems, wouldn't the house been handed over to you vacant?
The developer agreeing to let you take possession before conclusion of sale should have been at his own risk and for no rent!
The way I see it. I think you've been taken for a ride and perhaps it is time you alighted from this "bus". It is taking you no where.
I would simply move out and look for a house elsewhere. After all, you haven't paid any money apart from the rent and legal fees...
Cut your losses and headaches and move on
Nothing is real unless it can be named; nothing has value unless it can be sold; money is worthless unless you spend it.