According to a Blue Poster, Kalviery, early last year that wouldn’t work.
If you already have game time ongoing, the promotion doesn’t kick in until the 6 months kicks in it seems. The OP had 8 days remaining on their original subscription, purchased the 6 month subscription, and then canceled to prevent auto-renewal. (Edit: The OP of the linked thread.)
Essentially you need to be in an active 6 month subscription to qualify; canceling before the 6 month actually activates wouldn’t qualify. So OP wouldn’t have the mount yet, and thus couldn’t have lost it.