I am having similar struggle. Called BAEC a few times and not getting anywhere; sent email message to BA Customer service & ticketing department, still not getting anywhere.

Will try to keep this short. Booked tickets to Tokyo with 248K avios + $1.554 tax & fees, a few days later, saw another availability for another day of travel; cancelled this first booking. Learned the hard way that Avios does not credit back to the account fast enough. While waiting for the 248K avios to credit back, made another booking with Avios + money: 99,200 avios + $1,740 + $1,540 tax and fee. Within 24 hours, saw another availability that is better for us. And I called BAEC this time and they first helped credit back the 248K avios, then validated that I had the 443K avios needed to book the new flight. At that time, my account had about 333K avios, and another 99,200 avios that was tied to the avios + cash booking. After they did the calculation and confirmed that I have enough avios for the flight, they reserved the new booking, and advised me it could take up to 72 hours to confirm the reservation. Next day, received an email regarding change fee of $320 and called them back to confirm. Patiently waited and called a few times, finally after 6 days, the ticket department confirmed the booking. They have charged $320 change fee; credited the 99,200 avios then immediately charge that + 333K avios, a total of 443K needed for the new booking. But they did not refund me the $1,740, the cash portion of the prior booking made with avios + cash. I have called them a few time since then, and they told me there will be no refund. And I said, you charge me the full amount of avios needed for the new booking so why kept the $1,740? And that does not make any sense if I have enough avios. As this booking is all avios, not avios + cash.

Trying to figure out whom else to contact to get this resolv