Confirm who serves the meter first
The service-territory check answers the first Duncanville question: who owns the delivery relationship at the meter? For the addresses covered by this guide, that context is Oncor Electric Delivery. Retail competition occurs on top of that delivery system, so the customer can select a REP without changing the TDU.
Municipal boundaries and electric boundaries are different datasets. A Duncanville mailing address near a territory edge can require a separate verification step. Confirming the utility before comparing price plans is faster than discovering at enrollment that the selected offer is unavailable.