They have sourced oil from other places, Brazil, Canada, they are still getting shipments from Iran even with the so called Blockade.
Keep in mind we have only 15 ships trying to control a lot of water and that is in the Gulf of Oman, we have no ships in the Straight at all.
They are also further developing their own internal oil fields as well as off shore.
https://en.wikipedia.org/wiki/Petroleum_industry_in_China
Additionally they have been stealing coal conversion IP for years.