I take 5mg oxycodone 1 or 2 tabs every six hours as needed I had a toxassure test and there was no osycodone in my system why?

What was tested? Was the test specific for oxycodone? A generic screening test for opioids may not pick up oxycodone.
Key is as needed. Perhaps you did not take the medicine for a while. You wrote you use it as needed? Perhaps it was not needed before your tox screen test. Hope that helps!