Agree with PoTreeBoy. If that doesn’t get you anywhere, might consider the possibility the clutch is sticking.
I have zero experience with that model tractor. Grew up running my Dad’s old Ford that had a clutch that would stick semi-routinely. Push the clutch and if it had a nominal load on it, it would keep going. Hit the brake(s) while keeping the clutch depressed and it would break loose and stop with no problem. Of course if it was under a load, it didn’t stick. Worst part was if it stuck when it wasn’t moving there was no way to get it in gear without breaking the clutch loose. Fortunately the hydraulic pump was on the transmission side of the clutch so if you ran the 3 point all the way up while holding the clutch pedal down, it would break loose when it maxed out at the top.
If that’s what it is, I’d tell you how to fix it, but I have no clue. Ran it that way for around 20 years and it mysteriously stopped sticking.
Of course if you hit the clutch and brake and it still doesn’t stop that sounds pretty dangerous so hopefully it isn’t doing that.