I tried Hydrogen Peroxde and oxy clean, and it worked for me. How long did you soak it? What percentages did you use? I would recommend soaking for 7 days or more, depending on the amount of yellowing to be found.
I would recommend to keep soaking it. Try to get in sunlight if you can, as I have read that some UV radiation will speed the process, though this has not been verified, as far as I have seen.