Are you booking advance rates, or advance prepaid rates? Sometimes it is not readily apparent when making the res - if you read closely, the first states (something along the lines of "XXX day advance rate". You will then need to look at the cancellation policy - but generally, there is one. The second reads "XXX advance rate, no changes, no refunds etc etc). If you look at the cancellation policy, you will find there isn't one - somewhere in there it will mention the no change, no cancel, no refund stuff again.

My thought is you were booking the first (but thought that) you were booking the 2nd.