Being open and honest with your subscribers about whats happened which you've already done is good. Aside from that just have to push through it, keep making content and eventually it'll stop or you're subscribers will outweigh the dislikes. It all helps your video gain more traction so if anything that's some positive to take away. It sucks but you'll get through it
Damn, that sucks man! I guess there's only 2 things you can do in a situation like this...
1) cry in a corner
2) keep uploading, and power through it. Don't mind about the analytics
(I would probably recommend #2) xD
But on a serious note, don't take any action towards it. The botter will probably get bored and leave you alone after a while. Just keep uploading the same quality videos and I'm sure it'll get better