The same thing happened to me more than once. I had to get the well driller back to flush out the well. They pumped 2000 gallons into the well, shoving some of the mud back where it came from and percolated much of it out the top. Then they tossed in a bit of stone and called it done.
I did manage to unlock the rotor but the pump was never the same since. I used the old pump to wash out a lot of the mud that came up again and developed the well which was something the driller never did.
So, is all 120 feet casing through mud or is there a rock bore at the bottom?