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I sold my previous house & property under a owner finance/contract for deed. In the contract it states that buyer must pay all taxes to seller on or before Jan 1st of each year until contract is paid in full. I spoke to the buyer today and he is now stating that he is not going to pay the taxes. What do I have to do to get him off/out of the property so that I can resale it? 
Talk to your attorney immediately. Take all contracts that you have between you and the buyer. This would be considered a breach of contract. However, you need to have a lawyer advise you what to do. That's their job, especially litigation/Real Estate Lawyers. You should be fine. It's just a matter of how long it takes to squeeze the money out of him and/or get him out of the property.
If it is stated on the contract, an Attorney is the way to go. for that tenant, it is just a matter of time.