Writing is a medium of communication that represents language through the inscription of signs and symbols. wikipedia.org

Customer service is the provision of service to customers before, during and after a purchase. wikipedia.org

Customer support is a range of customer services to assist customers in making cost effective and correct use of a product. It includes assistance in planning, installation, training, trouble shooting, maintenance, upgrading, and disposal of a product. wikipedia.org

A call centre or call center is a centralised office used for the purpose of receiving or transmitting a large volume of requests by telephone. wikipedia.org

Technical support or tech support refers to a range of services by which enterprises provide assistance to users of technology products such as mobile phones, televisions, computers, software products or other electronic or mechanical goods.

A sale is the act of selling a product or service in return for money or other compensation. It is an act of completion of a commercial activity. wikipedia.org

Cold calling is the marketing process of approaching prospective customers or clients, typically via telephone, who were not expecting such an interaction. wikipedia.org