Well, the fault appears to be your own, as I have never had this issue and I have cancelled my award nights willy nilly and sometimes I have noticed -- as others have -- that they do not go back into the "bank" automatically -- this happens rarely but it does happen, and those who actually monitor things catch these issues.
I assume that must have occurred with respect to your 2 award nights.
You must have made an initial reservation that you cancelled and it did not go back into the account and then the 2nd award night was issued to you.
Note, however, I have just observed -- and posted to FT -- that the overlap of the 2 free nights is very small, about 7 - 10 days, so you were obviously cutting things very close -- hence you should have monitored your account better.
Hopefully you will learn from this lesson and not trust computer generated cancellations inherently. @:-)