I think you should message Kawacy before you use their picture as your cover. If you had and Kawacy didn't reply, that means you should not. You somehow already have a big follower base, they won't care anyway if you change the cover.
Webnovel saying "It's fine" does not matter. They are not Kawacy and do not legally own the image, nor actually have right to allow you to use the image. Plus, they have been using images of other artist without permission for advertisement.
Also if you can chill out and say, put more time into polishing your finished chapter instead of making a new one like a machine, you would probably has less need of a proof reader.