Angry with client

A client has not paid for our service because he thinks he shouldn’t have to or that he has been ripped off. I called him to try to discuss it but he didn’t want to go into the details, said he would pay but still hasn’t.
I had coaching on my feelings about this but now when I think about it I still feel really angry. Maybe initially I felt attacked and fearful but now it is anger.
C He hasn’t paid
T He thinks we ripped him off but he is ripping me off!
F Outraged
A stew on it, talk to him in my head, get stuck on it, resist the anger and push it down but it comes back up
R the result is I’m stuck on this and I’m stuck feeling the anger, I’m ripping myself off?
My question is how do I move past this?
Am I still stuck because I’m trying to think my way out of it instead of going through the feeling and letting it be. I’m conscious of trying to resist the anger because the anger feels bad. I don’t want to live a life filled with anger. And especially going to work feeling angry with clients doesn’t serve me.
This happened 6 weeks ago but I guess it has come up now because my employee told me yesterday he still hasn’t paid.
Maybe I’m not stuck, maybe this is just new anger with a new thought.
What is your advice?