I have two flights that I am changing the date/time only (by only one day). BA issued DONE ticket but they are internal QF flights.

I am being told by BA that there is no availablity for the revised dates for either flight yet QF site shows them as being available to book for cash at the same cost as my original dates. [I'd also note that its a DONE fare but my original booking was in Y as there is no J on the routes in question]

Any thoughts on getting around this ?

Thanks