Can't pair new phone to bluetooth

I just replaced my phone with a new one. When I tried to pair the new phone, it ask for my passcode???? I tried 0000 and 1234, but neither numbers worked. How do I find the existing passcode that I was using with the old phone? Got a replacement phone, unpaired from old phone, new phone can't find the headset. This has happened twice now, the first time I got the replacement Instinct I just bought a new headset, but that is getting old and expensive. Why can't the new Instinct detect the headset? I have unpaired it from the old phone.