Qatar Airways

Hi, I booked Qatar airways flight from Toronto, Canada. But that flight has a connecting flight from USA. I did not know that I need transit visa of USA for even connecting flight from USA. Now I want to cancel my booking. But I could not find any QATAR air ways office in Toronto. You can find office address online, but in real when you reach at that address, they will not allow you to enter the building. For God sake, is there any body in QATAR airways who can help me??? Thanks.