Unable to get through at various points today using the gold line or the number on the cancellation email (both too busy / cut off).

However I just tried the gold line at 18.30 BST and got through immediately. Dealt with very efficiently by a friendly agent and my Avios and 241 voucher were back in my account straightaway - I was told the waiting time for the cash element to be returned would be 14-21 days however.