Can I contact Yahoo.ca (email/account) support by email?

The above people are correct you could change your password, but also you could have spyware or a virus that is allowing people to see your computer when you are on it. First thing would be to change your password and even have a backup email address just in case you can't use your other one again. You should maybe download an anti spyware program that removes anything that could be malicious on your computer. A couple of good ones are Adaware and Spywseeper. Cheers!