Customers who try to avoid paying bills are not classy or to be loved because they are not following through with what they agreed to and are essentially stealing from the company.
Consider the statement "A customer is refusing to pay a bill because they claim it has already been paid but cannot provide any proof of doing so.". Based on this "I just love the customer who is trying to stiff the company by refusing to pay the bill and pretending that it has already been paid, how classy." a true statement? Yes, no, or I don't know?