I cancelled my flight by mistake

Long story but I will try to be as concise and to the point as possible.

I booked YHZ-YYZ-LAX

Sometime after booking, AC changed the YHZ-YYZ segment to a 0515 departure.

I call AC to inquire about changing that segment to the evening before, overnight YYZ and then take originally scheduled flight from YYZ-LAX

Booked economy comfort fare

While on hold with AC, recording suggested (directed?) me to avoid waiting on hold and simply make the flight change myself online.

I attempted to do this but somehow managed (or AC managed) to cancel my YYZ-LAX flight in the process. They refunded me $100.00 automatically.

I immediately got on the phone to AC as soon as I realized the mistake (which was mere minutes afterwards)

AC representative told me there was absolutely nothing that Air Canada could do because the changes were made on the web and not on the phone.

In order to rebook my YYZ-LAX flight, I had to pay Air Canada an extra $1200 because of my (or possibly their) mistake.

My question is quite simply, do I have any recourse?

thanks