Changed ticket online with no fee: then asked to pay by agent
I have a mint ticket, lax-Bos that I changed online yesterday. It was a time change to a later flight. I went through the process and no add/collect was solicited. (I think when I first bought the ticket, I had status. Perhaps that's why?).
But at the end of the online process, I was directed to call B6 because something "went wrong."
B6 agent tells me I owe $75 for the change. I say "never mind, please put me back on original."
After we finish, I go back online and change ticket again. No fee solicited. Same error at end. I log out and log in. The reservation looks fine. I have an email confirmation.
Any insights here as to what transpired and what I should do?