pay in full, pay, settle, discharge, meet, clear, square, honour, satisfy, make good, liquidate

get one's revenge on, be revenged on, revenge oneself on, repay, give someone their just deserts, reciprocate, punish, avenge oneself on, hit back at, get back at, get, get even with, settle a/the score with, settle accounts with, pay someone back, retaliate on/against, take reprisals against, exact retribution on;

let someone see how it feels, give someone a taste of their own medicine