Tex. Ins. Code § 1452.107

An enrollee in the managed care plan is not responsible and shall be held harmless for the difference between in-network copayments paid by the enrollee to a physician who is determined to be ineligible under Section 1452.106 and the managed care plan's charges for out-of-network services. The physician and the physician's medical group may not charge the enrollee for any portion of the physician's fee that is not paid or reimbursed by the enrollee's managed care plan.