"Thank you for getting in contact about the Avios Booster promotion.
I have been in contact with the relevant team and they have advised me a system issue occurred with the edit button when members were changing their multiplier selection during transacting.
They have advised to fix the problem and get to the desired amount is to use the refund transaction link in the email confirmation which will revert the Avios and trigger cash refund.
The edit button function has now been fixed, so please try to make the transaction again and chose the desired x3 multiplier when doing so."
Unfortunately I can't refund the transaction, assumingly because I had to spend the Avios that are on my account for a flight (That was the whole reason I boosted). Got to pick your battles with BA and this is one that I really cannot be bothered with. At least they responded quick enough!