I am so sorry you had such a rotten time and that you haven't yet been credited with the refund
but
when you booked the tour, the small print in the blurb does say 48 hrs cancelletion
If you need to cancel within 3 days of your holiday departure date, please speak to the shore experiences team once you’re on board. Cancellations cannot be made via My Cunard at this stage.
Once on board, if you need to cancel your shore experiences before the cancellation deadline (generally 48 hours before the ship’s arrival in the relevant port) a 10% cancellation fee will be applied to your on-board account and the full amount paid will be refunded to your original credit/debit card. In order to process any cancellations, tickets must be returned to the on-board shore experiences desk.
We regret that we’re unable to refund the cost of experiences cancelled after the cancellation deadline. If you do need to cancel after the deadline, we’ll credit the original credit/debit card you used with the full amount you paid, however, a 100% cancellation fee will be added to your on-board account.
and although this doesn't absolve Cunard for the delay in crediting your account once it was approved, it does show that they didn't have to give any refunds for the late cancellation.
Hopefully, you'll receive the refund soon.