My volume knob won't turn at all. Help! :(

My volume knob has decided to stick and not
budge. Originally it worked totally fine, albiet the
plastic knob was broken off so I had to turn the
metal peg instead of a knob. I was at the junkyard
the other day and found a replacement knob, and I
tried to fit it on but it was the wrong size. Before I
realized this I tried to press the knob onto the
metal peg and it was supposed to click in. When it
didn't I applied a lot of pressure, not a ton, but a lot,
and I may have heard a snap or crack noise. After
that my volume and balance control (they are on
the same knob, the volume is controlled by a knob
and the balance is controlled by an outer ring) kept
on turning each other. I could hold the balance in
place to change the volume, but it was difficult. I
was playing with it trying to get them to stop
turning simulataneously, and the volume knob got
stuck when I moved the balance all the way to it's
maximum and tried to turn the volume knob to the
right. Something happened and now the knob
doesn't turn and is stuck on. Can you let me know
what happened and how to fix it? Should I try some
WD40 on the metal peg and use pliers to turn it
and hope for the best? Should I use pliers to pry
the metal peg outwards to see if I pushed it in
somehow? I really hope I don't need to replace the
head unit. Thanks.