I am at the same situation. I canceled my award booking in February and milage back to my account immediately but taxes refund still haven’t credited back to my credit card in April. So I called Aeroplan and they said they already send taxes refund request to Air Canada and they can only open a claim for me again. I called Aeroplan agin at the end of May and Aeroplan said they cannot do anything. I finally gave up calling Aeroplan or Air Canada and called Amex to file a charge back. I successfully got the money back last week!