If I'm understanding you correctly, you sold the house and provided the financing to the buyer, The paperwork for the sale should probalby have been recorded by you, rather than the buyer. If they buyer isn't paying, what you need to do is a foreclosure to take the property back before you can re-sell it. Talk to a lawyer to make sure you do the process correctly. It' not very expensive, especially compared to creating title problems for yourself.
BTW - Most mortgages have a "due upon sale" clause that essentially calls your own mortgage due if you sell the property. There are further restrictions in your own mortgage that further prevent you from allowing anyone else to have an interest in the property without your mortgage company's prior written permission. You basically can cause a default in your own mortgage by doing what you did - regardless of whether or not you are current with your own mortgage payments.
Furthermore, from your brief description, it sounds like you entered into a contract for deed with the party you "sold" to. While not illegal per se, contracts for deed are disfavored by Texas law, and their are strict requirements for reporting and providing statements, etc. to the buyer, with legal penalties for failing to carefully follow all of the requirements of the law.
You need to hire a competent real estate lawyer in your area to advise you specifically on the situation with the person you tried to sell to, and generally about whether or not you should try to do that again.
Interesting situation. It sounds like you sold a home on which you still owe money for a purchase loan (your mortgage). If so, you need to make sure that you continue to pay the mortgage note. If the buyer has failed to make payments to you, you need to write to the buyer by certified mail to provide notice of default in the manner specified in the deed of trust. For you to have a mortgage lien on the property, you have to record your security documents (deed of trust) in the county property records. You probably need a real estate attorney to help you sort out this transaction, and to keep the buyer from causing more trouble. If you still have a mortgage loan from when you bought the property, you have to be careful to avoid a circumstance where that lender accelerates the note and declares it fully due and owing.