No. When you’ve chosen a new deal, your new supplier will handle the switching process. They’ll contact you to let you know what date you’ll be transferred over, and they’ll contact you around the switching date to ask for a meter reading. They’ll pass this on to your old supplier so they can send you a final bill. You don’t need to contact your old supplier, as the new supplier will handle everything for you.
Then, in 2002, Texas deregulated the electricity market and everybody cheered! Except that, sure, deregulation opened up the market to competition that may (or may not) have resulted in lower rates, but it introduced a whole host of other issues. These issues may not have been factors before but now they’re critical when you’re on the look-out for cheap Houston electricity providers.