If you want to retain customers after they have witnessed poor customer service from your sales team, you must make phone calls and follow up on their reported problems. It is better if a higher authority of your brand takes the call and discusses the matter with the customer. The customers will feel assured that a higher authority is handling their query, and the company apologizes for their earlier behavior by a staff member. In this way, you can revive the customer experience in your favor and still use your chances to increase revenue from existing customers.