Have you confirmation from SIA that they have not processed your refund? Have you asked them for the refund Transfer reference number? Have you tried to telephone them in Singapore (much better than locally)?

If the answer to that is that you don’t have full and final reimbursement info, I would persevere and telephone them and get it. You will need it.

Because they are usually pretty efficient and after 6 months I would bet that your problem is not SIA, but your bank. Especially if you changed your credit/debit card and now have a new card with a different number on it to the one you used to make the reservation. SIA will have reimbursed your money but your bank will not have a record of your old card number linking it to you and your money will be sitting there somewhere between VISA/Mastercard and your bank. And your (Asian) bank won’t care a Brass fig about it or do anything about it unless you make a real stink.

Been there, done that.

Give it a try. Good luck.

AF