Who is the letter from? A debt collector or a law enforcement agency? If it is a debt collector, then find a TX FDCPA lawyer. They are likely violating the law by threatening action that they likely can't (depending on your state law) take.
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23 years ago? That is beyond zombie debt, that is simply frivolity. Yes, trying to collect past statute of limitations is a violation of FDCPA and the company pursuing your husband can be fined $1000 per violation. Keep a copy of that letter and document any further correspondence and letters. You guys may also considering hiring an attorney specializing in these matters if this keeps up. Good luck.
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Make a log book of the collection efforts and take it to a consumer rights attorney. Breach of contract is 4 years, hot checks for criminal liability are 2 years. A court in Texas cannot grant relief to the plaintiff or creditor, but may grant you relief if they are using improper collection methods.