Sounds like they were unable to locate the e-ticket on their computer? And then, without the printout, the easy way out was simply to BS their way through...

I try always to have a printout with me. Plus typically a pdf on my laptop.

This said, in the case of the OP, I would get real upset and I would do everything I can to have this rolled back. Starting with AC/Aeroplan while at the same time requesting my credit card to suspend payment of the extra ticket.