Hi, don't be dissapointed. The same thing happend to me. I just saw someone downvoted me without any reason and then I saw it's some bot or spam or fake account, or whatever. Try to report those accounts as spam to steamclearners. Those bots usualy don't have any voting power so they cannot do anything to your reputation.
Thank you very much for your reply! Can you please teach me how I can report to steamcleaners? I did not know about it!
http://steemcleaners.com/reports/new This is reporting room. Just put the link of the fake account and you can add in comment that you were downvoted by this account without any reason.
Thank you very much!