Reliant Energy offers a variety of payment options to make your life easier. Pay online anytime, day or night. Pay by phone call 844-637-5408 Pay by regular mail: Reliant Energy Retail Services, Dept. 650475, 1501 North Plano Rd., Richardson, TX 75081. Pay in person at a convenient location. To set up electricity service: call Reliant at 1-844-637-5408 and enroll by phone.