We run a small website which is related to IT certifications (career). The website has been very old (more than 10 years) and recently we observed that one important URL has been removed from the google results. When we give the title of the URL in google search bar, some other unrelated site is appearing in the google results in the place where our link used to be. The site has the same Title as our page. Further, we observed that this particular site is showing hundreds of back links to our site as per the webmaster tools (google), which I don't see physically when visited that site. Further, this site has nothing to do with IT certs or career. Is it some kind of hacking? How could it be possible without hacking the site?
Note: Our page is clean and not detected any spam or malware at least as far as we know.
Any suggestions as to how to get back the page in to Google, and how similar thing could be prevented in future?
PS: Already raised spam report with Google.