Some context regarding the issue for the op
https://www.flyertalk.com/forum/brit...l#post33419396
https://www.flyertalk.com/forum/brit...l#post33406318
https://www.flyertalk.com/forum/brit...l#post33401290

It seems this concerns a TA booking for 15 August for JFK-LHR-JNB-LUN rtn which had a flight cancellation. The OP wanted to rebook on another airline. I am not quite sure why AA/BA TATL and then QR to JNB via DOH wouldn't have been possible, my reading of the BA rebooking allowances is this would be possible. Tbh I am not clear why the TA didn't do this?

Also the OP has a FTV for a July 2020 booking for JFK-LHR-TLV which the OP now wants refunding, but I assume the OP choose to take a FTV.

EDIT: just to add, I think the $450 credit issue relates to the JFK-LHR-JNB-LUN booking which previoulsy had a flight cancellation and was moved to August, and that the flight on the new dates were cheaper. For an involuntary change usually there is no re-price, so you are not asked to pay more if the new dates are more expensive, but equally you don't get a part refund if the new dates are cheaper. With BWC now there is the option to go via that and get a credit if the new dates are cheaper. It's not an obvious route, and more of an artifact of BWC rather than being a deliberate policy. Some BA agents will do a quick check for the new dates and recommend doing it this way if they see the new dates are cheaper. Again, if this is a TA booking then the choice to do a simple involuntary change vs going via BWC is with the TA - both would be possible for the TA to do. The issue really needs to be taken up with the TA though about why they choose to do it as an involuntary change rather than a BWC change.