How to: I sent an invoice to a customer and they paid for part of it but never paid the whole amount

MusicBusinessOwner

I sent an invoice to a customer for a service and they paid for part of it, but never paid the whole amount. I applied the payments they gave me to the invoice. I am still owed $100. I know they do not intend paying the rest and I am sick of chasing them for payment and do not want to see this money owing every time I look at my unpaid invoices. I can't delete the invoice because I have already applied payments to it. What can I do? I will never get the money I am owed from these people. I just want it out of my list.