Iran decides who they sell their own oil to, not the United States

'Iran has devised initiatives to foil the US sanctions on its oil exports, Secretary of Iran's Supreme National Security Council Ali Shamkhani said, noting that the country has multiple ways to sell its crude'
https://www.tasnimnews.com/en/news/2019/02/23/1952845/iran-has-plans-to-neutralize-us-oil-sanctions-top-official