I bought a base fare at £500 and have flown the outbound. Tried to change the inbound to a week earlier and found the flight I wanted with the Premium Economy fare class that I was booked in originally. It wouldn't do the change online and the BA rep wanted £250 extra for the base fare.

Shouldn't the base fare stay the same if I am booking the same class for the new dates? She told me that when I booked the base fare was £500 and now it's £750. Anyway her computer was auto quoting the £250 base fare and £108 to change the ticket.

I thought that if I bought T class at £500 and then change the return after flying outbound my base fare is locked in for the return? Is she right in charging £250 extra for the T class thats for sale now?