Actually it was never called Oxygen. It was developed for the Oxygen cable channel before being picked up by The CW, and somebody who wrote an article announcing the pickup mistook the name of the network for the name of the show, and other sources quoted that article and repeated the error. It was always Star-Crossed.
Can you provide a link to that effect? Every outlet I've seen has previously referred to it as Oxygen
put an fka (formerly known as) Oxygen
in their mention of the title Star-Crossed
. Other outlets have also specifically mentioned it as a name change.