My two cents:
Kaori from that anime has a pretty generic design so I don't see much of a problem that they look similar.
I think the user who commissioned the works is the same user who sold the oc to you(as Chicha pointed out) but perhaps their dA account is inactive and they forgot to remove the drawings.
I disagree with thinking it is OK to use a character even though one has been scammed. In that case, it's very unfortunate but the buyer would have to sort things out with the creator(s) and maybe do an artist beware if the seller doesn't respond.
It is /not/ the designer's/artist's responsibility to grant permission to use if their design has been sold without their consent.
I advise doing a thorough research before buying adopts, and I'd personally always buy from the original artist than a reseller;;
Anyway I hope you can still contact them somehow and it works out for you bun--!