Booked a 2-1 on ba.com (Dec 2019) and had to cancel as had re-scheduled twice but could not do again as it would have been over 1 year since original booking. Cancelled over the phone (in October) and received the refund on both tickets together exactly one month later. As previously mentioned, miles and 2-1 voucher were re-credited immediately so no idea why you have to wait a month for the funds which should also be immediate if it was originally a ba.com booking, ba only flights etc etc.