I would take the matter to CEDR if you have not received payment. There are a number of cases where payment to overseas accounts have not happened or been badly delayed. If you are able to supply a UK or other European bank account - maybe a relative or trustworthy friend - then I would do so. I haven't seen any reports of problems with Canada bank accounts either. The other option is to suggest on the CEDR submission is that you ask for a BA voucher, which can be used like an Amazon gift card, assuming you have future BA travel plans. If you are not prepared to call BA (and there is a local number in Japan) then I can't see an alternative to CEDR.