Almost sounds like you've cross-threaded the nut that presses the collet together to hold the bit. I say this because actually hitting the wrench with a hammer should do SOMETHING.
If I'm understanding you correctly, you can't loosen the nut, because there's no wrench (other than a basin wrench, and you certainly aren't using that) that you can use on the collet itself.
If it's NOT the nut, and you are meaning to tell us that the collect can't be lifted out after loosening the collet nut, then you need to use a needlenose pliers or some other such item to get under the flange that is typically on the top of the collet.
Something to remember as well - routing heats up the bit, which in turn heats up the collet. Any debris in there will make the bit almost impossible to remove. You can take some emery paper to clean off the surface of the shank of the bit prior to putting it into the collet. Also, DO NOT bottom out the shank in your router. You should have a gap of an eigth of an inch or so. Not doing so can make your bit next to impossible to remove. Invert an air can (like for blowing crap out of your PC) and spray. Use some gloves and then try to pull the bit out of the collet. It still might resist, but you should find it a lot easier (and the gloves will help you keep more of your skin should your hand slip

)
Tell us if what you're saying is that the nut won't come loose or if the nut is loose but the bit won't come out of the collet.