Originally Posted by KathyWdrf

Were the prior trips (where you were able to make the change) booked in a different booking code, such as a fully refundable one?

You need to familiarize yourself with the fare rules -- the fact that you have omitted this information implies that you have not heretofore paid any attention to it. Leaping to the conclusion that it is somehow the CSR's fault that they won't make the desired change (as suggested by the thread title) is unfair.