I want to make a complaint about the service and the service I received over the phone. How do I do that

Taking 3 weeks to process a payment.. when I called they said it will be in my account in 24-48hrs when it wasn’t I called again and they said it will take another 5-7 business days. I have lost jobs because of having to continuously push jobs because of payment not being received.. and my client is very upset because I keep pushing their job as well.