What you need to do to protect your self is to have the person to whom you gave the money order acknowledge that they received it - and what ever other facts that they will admit to - and that the bill is therefor paid.  The person should sign the paper work that is prepared and quite possibly do so before a notary and other impartial witnesses.   Once the person acknowledges that the bill was paid by you but that the money order was destroyed by them and through no fault of your own then you should be in the clear.  But a verbal agreement with out proof from wither of you is not good for you.  Good luck.