Correct - as noted above, the OP is entitled to the downgrade refund. As mentioned too, they may need to find for it as BA are notoriously bad at paying downgrade refund and will try to just pay a "difference in fare" instead which will most likely be disadvantageous. But the refund is due and the OP should ask for it (in my earlier post, I suggested referring to the main thread so they can have a go at calculating the refund due based on the Mennens formula as it is not straightforward and I think chances of getting it are higher if you correctly calculate what you are due and specify it).