My Facebook account says I liked many pages that I didn't even know about.  Even though I click unlike, they still show after I refresh the  page. I have tried changing my password many times, but it doesn't change. How can this can happen? How can I fix it?

I think you mean that you see posts of the pages which you haven't liked. It probably because the people who are your friends like the post of that page or they are regularly tagged in some of the pics of that page. It may be also because of you constantly liking the posts of the respective page. If you don't want to see the respective page posts either you can do the following : Click on the downward arrow beside the post. Then click on Unfollow the respective page. Hope it helps !

Delete any authorized app tokens, trojan apps from your device, kill all sessions.Install extension like Noscript to prevent likejacking.Install malwarebytes, that's all you can do.

Try to report problem in Facebook. You can also ask for help from Facebook. The help option is available at the downward arrow in the top .

This problem can be sort out by just single click on unlike option if its not done then report a problem to the Facebook.The only solution is to report about your problem.Also, make a strong password so that no one hack your e-mail ID.