The abstract noun "song" can be expressed with the verb "sing." Alternate translation: "But now they sing songs about me to taunt me" (See: [[rc://en/ta/man/jit/figs-abstractnouns]])
Here "byword" is a metonym for the person about whom people make cruel jokes. Alternate translation: "I am now one whom they make cruel jokes about" or "They joke and say cruel things about me" (See: [[rc://en/ta/man/jit/figs-metonymy]])