How Long Does Oxycodone Take To Be Completely Out Of The System?

I need oxycodone for chronic pain. I was going to a dr. and getting 120ct. 10/325. I went there for three years but failed last drug test from going to a party and drinking and did something else I shouldn't have done. I was told it would be out of my system in3 days and it was 8 days later. can you help