Why do I keep getting random friend requests?

Every time I log in I have a friend request from some random user I've never heard of. Their names usually comprise of three random words put together (obviously it seems like a bot made these). I remember sometime last year I did accept one of these random request and it was one of those Elo boost bots trying to sell me elo boosting services. Of course I deleted it but now over the past few months I just get these random adds. I didn't log into league for about a week and I came back and I had 15 new friend requests. All with random 3 word combination usernames. Is there any way to stop these? :c