I managed to book two seats LIM-CUZ-LIM a couple of months ago for August this year for avios+cash. I now want to change it but the ba.com gives me error message every time I try. I thought I make a new booking but Cuzco doesn't seem to be accepted as a destination airport.

Has anyone experienced the same? Will it allow me to change the date? I obviously will need to call and was wondering if the off-line fee will be waived? I'm currently Silver.