turn the knife

To add to, exacerbate, or amplify a betrayal or wrong by further malicious actions. He said it was over, and then he turned the knife and said he had never loved me.

turn/twist the ˈknife (in the wound)

deliberately remind somebody of something they are already upset about, and so upset them even more: After the divorce, her friend turned the knife in the wound by saying she had always thought that the marriage wouldn’t last. ♢ All right. I know I was stupid. You don’t have to twist the knife.