Dave and Sue wrote:
The cables are really almost impossible to break
It really sounds to me that the OP has a slipped cable.
Meaning it has come out of the valve.
I would cut the under belly as needed or just take that panel out for full access.
They are not hard to replace,just hard to get to.Good luck
Agree with "slipped cable".
Replacing the cable sheath into the housing & set screws on the cable at/to the existing valve isn't too bad.
Same for replacing the cable assembly - leaving the existing valve in place.
However, for replacing the entire valve, it *can* be hard to get to *AND* hard to replace - depending on the location of the piping...:(
.