What should I do if the seller of a land contract refuses to give me an account balance statement or escrow account balance statement?

You would have to sue the land contract owner in civil court. With a land contract, you should have been given a payout schedule with each of your total payments on it. If you have paid more (or less), but the holder of the land contract will not turn over that information, you would have to file a claim in civil court to either terminate the land contract or seek a court order for the holder to turn over that information.