If you have had it under contract and you have a due diligence clause(hopefully you do) and it is apart of your diligence list items that you have financials, then they are legally obligated to give it to you otherwise theoretically your contract should have never started therefore you have until forever until it begins. Of course this is if your contact reads that way.
Another way to convince them is that if you have it under contract you need that to close the property and therefore they can sell it. There probably getting a little sellers remorse and thinking they could get more than what you have tied it up for. Not sure though.
Also you could just have an open conversation with them and be like what is the deal...if you have it under contract your not going to blow up the deal because it’s your right to purchase it. Just be very open you want to close and be like cut the ********. What’s the deal. Maybe phrase it in a nicer way but this happen more than you would think.
And if all else fails...play hardball and tell them you’ll tie up forever and they’ll never be able to sell it because you’ll just sue, blah blah blah....etc
This is all assuming you have it under contract