The refund was issued on August 12, and everything looks good on our end as far as I can tell.
Please check with your bank again - if you own multiple credit cards, perhaps it would be prudent to double-check (via a Support ticket) which card was used to make the transaction.
I don't think I've heard of a refund simply not going through, and I've worked Support in GOG since beta :), so my only reasonable guess would be that perhaps you used a different card than you remember, back when you preordered, and therefore maybe you're checking the wrong account balance, and are asking the wrong bank abou the wrong card?
If needed, we can open a support ticket with our payment provider, but those can take a long time to process, so I'd like to rule out the above possibility first. :)

Dear nonetheartist,

Just as my colleague said in September, the refund has been issued on our side on August 12th. As I can see in your ticket history, we contacted you on August 28th. The message included details about possible cause, suggested solutions and we asked some additional questions. The ticket's status is "pending" since then, meaning we never received a reply from you. Because of that, we are unable to decide what steps we can make next.

I kindly ask you to reply to your ticket, so we can stay in touch with you and work together on the solution.
If you have any additional questions or complaints, please contact me directly via GOG chat.