I bought a Fantom Uno several weeks ago new. It has a flip flop hub. I've wanted to put a smaller sprocket on the fixed side. I've removed the locking ring, but can't get the sprocket to budge at all. I've pulled on my chainwhip tool as hard as I can. I've tried to force the cranks with my front wheel against the wall, and nothing happens. When I first bought the bike, I could feel the sprocket seating in the backward pedal direction. Any suggestions for breaking this free?