After you delete the double post,
go to the Cub cadet web site and download the owners, service & parts manual for your mower . You will need the numbers from the ID tag under the seat to ensure you get the right one.
Deleted cause this bit was wrong, silly me
Dissengage the transmission ( see owners manual ) and try to push the mower.
If it rolls back & forth a few feet without a wheel locking up then the brake is not locked on.
Now re-engage the transmission, it should be a lot lot harder to move in both directions and stop the instant you stop pushing.
If it rolls with very little resistance then the tranny could be gone.
Get back to us with the results