Legally you are obligated to sign all documents to be recorded on your property that will need to be prepared at the bank's expense since it was the entity that erroneously signed a full conveyance of the paid of mortgage (or trust deed) on the wrong property that you owned.If you do not agree to do what the bank wants done as a result of its mistake, it will most likely file a lawsuit against you to reform and rectify the error that it did as an equitable matter.If you do not do so, you will be faced with having to defend the likely lawsuit. I suggest that you retain an attorney and negotiate with the bank for a better interest rate on the loan evidenced by a promissory note secured by the mortgage (trust deed) with respect to the one that was inadvertently retired. That way you receive a benefit as well.