I Take Oxycodone 15 Mg Four Times A Day And

I take oxycodone 15 mg four times a day and I recently took a urine analysis test and it came back negative for oxycodone. Basically, my doctor told me the test showed that I am NOT taking my oxycodone, even though I know for a fact that I take it every day. I want to confront him about his test being faulty, but I do not have the evidence or know enough information about why the test would not show the oxycodone.