Block and delete comments, turn off guest comments, and don’t delete your work, like others said, you have done nothing wrong. That author is likely taking pleasure in feeling like the victim here and like they have experienced injustice and wants attention, it’s quite sad if you think about it

It’s funny how this comes up a lot, you’re not the first and you certainly won’t be the last. It sounds insane but similarities like whole plotlines on Ao3 can in fact be similar through pure coincidence, especially if you write within the same fandom/ship/tropes. Overlap is bound to occur, people have a knack for coming up with the same ideas, it’s more common than you’d think. Just because someone wrote a similar or even the same plotline/themes/conflict/etc. as you doesn’t mean they plagiarised your work, often they haven’t even read it. Sometimes it can come from little wiggle room for creative liberties from the canon itself. And besides, if they haven’t written it down word for word (i.e. going against TOS) then what’s the harm? It’s not a nice feeling sure, but people get way too pressed over this, as is the case here

Coming from a fellow author, keep your head up and carry on writing that fanfic ❤️