Canadian Tire

I booked an appointment for engine heater installation and car mechanic took over my car, saying that it will take an hour or more to install the piece. After an hour of labour he called me to say that I already have engine heater and that there is nothing to be installed. I wasn't aware of that as this is my first winter with this car that I purchased a year ago. He charged me $77.26 for "checking the wiring and testing the blockheater", as stated on the receipt. I argued that this is too much for that type of work but he insisted that it is not. I would like to get my money back as no extensive labour was preformed, especially not in this ridiculous amount. Please let me know how to proceed further with my claim to get reimbursed. Thank you!