Unfortunately you probably don't have much of a leg to stand on - the booking class is stated quite clearly on AC's online booking page at the "Review your itinerary" stage (under "Fare type") and the eligible classes are listed on the "Earn miles" section of the DC website. As a general rule, Tango fares do not earn any miles except for Aeroplan members, in the way that cheapo NZ fares often only earn miles for their own frequent flyers.

It's a pain, but not an unavoidable one I'm afraid. Shame you didn't catch it before you flew. I just booked LHR-LAX on NZ and the booking engine didn't tell me the fare class until it was confirmed, when I discovered it didn't earn any miles. A quick call to their call centre, £40 extra paid, and they had put me into their lowest mile-earning class.