you don't give a great amount of info here.
If you have a mortgage protection policy, then if you cancel, you get nothing back. You have used up the premium in that the insurer took the risk that you might die within the period of cover. You did not (thankfully) and therefore the money is spent.
You may have a whole life policy, which is much the same as above, you cancel, thats it.
You may have a savings element built in. If that is so, then you probably will get something back.
Downside of cancelling is, have you enough cover to pay off the mortgage if you died?
You are wrong to say that you have two policies on the one property. The policy is on YOU and possibly on your SPOUSE as well. You can have as much policies on your own life as you can afford or desire.