you cannot tell them anything. you have to act in an empathetic way that changes their attitude. You have to acknowledge their complaint; apologize sincerely; and, in the most kind way possible, offer to help them solve their problem.That is how you can change their attitude while at the same time ensuring they come back as a customer.some people are better suited at this than others. I am horrrible at it. i want to rip their head off and it usually come across that way.
Refuse service to them