Happened to me too!
What a joke. I just published my first paid app on the appstore. There's a really popular app that is really low quality (popular because it's the only option), so I made a better app and published it. The other app's developer spammed their own reviews with 20+ 5-star reviews.
Once I published, I got spammed with 20 1-star reviews! I did some research, and the other developer's website is registered to a ***** from *****. He also purchased the app from me. An hour later I got 20 1-star reviews. What a dirtbag. I emailed Google Play support through their form, but I don't have much faith in Google's customer service. This is really pissing me off.