The Affordable Care Act is run by the HealthCare.gov.  HealthCare.gov is a federal government website managed by the U.S. Centers for Medicare & Medicaid Services.

Contact Address:
U.S. Centers for Medicare & Medicaid Services
7500 Security Boulevard
Baltimore, MD 21244

AffordableCareAct.gov is not an active website.  Users should go to HealthCare.gov.
Obamacare.gov is not an active website.  Users should go to HealthCare.gov
ACA.gov is not an active website.  Users should go to HealthCare.gov