I am not an Attorney by any means. I am a licensed Associate Broker. I would need more information such as did you make an offer on a Bank Foreclosure? Is the property HUD owned? Is the property Private-owned/seller (not a bank)? Are you working with a Realtor who represents your interest such as a Buyer's Agent? Was the property private-owned/Seller but the Seller is trying to get a "Short Sale" (where the lender takes less money than what is actually owed on the current mortgage(s))
More details would be helpful. Did you put a response by date on the Purchase Agreement?
In the instance of a "Short Sale" the process of an accepted offer can take as little as 2 weeks and at most 3-4 months to be approved. If you are represented by a Realtor pease discuss the process with them.
In the instance of a Foreclosure it could take as little as 24 hours and at most 2 weeks, depending on the Seller/Lender.
Suggest contacting legal services/Attorney to find out if you have any recourse.