Here "Pay back to them" represents punishing them. What they have done can be stated clearly. AT: "Punish them, Yahweh, according to what they have done" or "Yahweh, they have made me suffer, so please make them suffer" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-explicit]])
Here the "heart" is a metonym that represents their attitudes and emotions, and being "shameless" means not feeling ashamed of their sins even though they should. Their not being ashamed would give even more reason for God to punish them. AT: "You will let them feel no shame for their sins" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The abstract noun "condemnation" can be expressed with the verbs "condemn" or "curse." AT: "Condemn them" or "Curse them" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])