Tex. Civil Practice and Remedies Code § 16.038

(a) If the maturity date of a series of notes or obligations or a note or obligation payable in installments is accelerated, and the accelerated maturity date is rescinded or waived in accordance with this section before the limitations period expires, the acceleration is deemed rescinded and waived and the note, obligation, or series of notes or obligations shall be governed by Section 16.035 as if no acceleration had occurred.

(b) Rescission or waiver of acceleration is effective if made by a written notice of a rescission or waiver served as provided in Subsection (c) by the lienholder, the servicer of the debt, or an attorney representing the lienholder on each debtor who, according to the records of the lienholder or the servicer of the debt, is obligated to pay the debt.

(c) Service of a notice under Subsection (b) must be by first class or certified mail and is complete when the notice is deposited in the United States mail, postage prepaid and addressed to the debtor at the debtor's last known address. The affidavit of a person knowledgeable of the facts to the effect that service was completed is prima facie evidence of service.

(d) A notice served under this section does not affect a lienholder's right to accelerate the maturity date of the debt in the future nor does it waive past defaults.

(e) This section does not create an exclusive method for waiver and rescission of acceleration or affect the accrual of a cause of action and the running of the related limitations period under Section 16.035(e) on any subsequent maturity date, accelerated or otherwise, of the note or obligation or series of notes or obligations.