Seems that you are the buyer of the property - so are you being asked for more than in the contract? This would be OK if the contract had been signed but NOT DELIVERED yet. BINDING acceptance in Wisconsin only occurs after the contract is executed (signed) by all parties to the contract, AND DELIVERED as set forth in the contract. So, if the contract had not yet been delivered, and the seller got another offer, it is possible that the seller could ask for more money via a counter-offer, or multiple counter-offer.
If the contract was delivered to you - then it is a binding contract,a nd can only be changed by mutual amendment of the parties.
Good luck! If you can't get satisfaction with this, it is a good time to check with an attorney.