You are faced with another call to this slow-paying customer which you are dreading because it always seems a waste of time. No matter what you say, the customer rarely responds with a positive answer or a payment.
What can you do except go through the motions again?
There is a great deal you can do, but it comes down to your attitude and state of mind. If you believe there is nothing you can do, then probably, there is nothing you can do. It is as simple as that unfortunately.
However if you truly wish to be good at your job, and equally important to get this client to pay your invoice(s), then here are some ideas which may assist.
Review your notes on previous conversations and your "gut feelings" about what was said by the customer. If your notes were taken properly, you may get some ideas on how to approach this next telephone call.
You could also ask another employee for ideas on how you may approach the situation. Perhaps your fellow employee might have some ideas. Furthermore, don't dismiss the idea of having a chat with the salesperson responsible for this customer.
Talk with the boss or your manager and see if they have ideas or can offer support.
At the end of the day, it is your job to make the customer pay their account. Starting each telephone call with that sinking feeling there is nothing you can do, only avoids the potential for success.
Dealing with the slow-paying or recalcitrant customer is part of your job. If you can learn to deal with these types of customers successfully, you will become better at your job overall.
From another perspective, you may go from one of those people who dread their job, to one who actually enjoys these challenging customers and finds another level of satisfaction within the work itself.