So, a ticket was issued, and when you phoned in, you got the PNR.

Presumably you no-showed the flight, now you're looking for a refund? I presume what they've offered you represents taxes/surcharges that they don't have to charge since you didn't fly, rather than simply 20% of what you paid.

AC didn't fail to issue your ticket. For one reason or another, you didn't receive an e-mail confirmation, but everything you've said suggests you could have flown if you showed up on the day.

I don't think they owe you anything other than a refund of whatever taxes etc are refundable, which is probably what they've offered. You can't just no-show a ticket and then claim a refund because they didn't send you an e-mail. Especially since you phoned in and got the PNR (and they'll certainly have a record of the phone call), so there's no way you can claim you didn't know you had a ticket.

If AC gives you a refund, please let us know, because I have a feeling my confirmation e-mails are somehow never going to be received on any of the non-refundable fares I decide I don't want to fly...