Internet provider that serves my area switches off the Internet at 12PM every day, and I have to contact the support team to make them to re-enable the services for me. As I have a big kind heart, I don't act aggressively because I know that the tech support is a front line that deals with all kinds of negativity and keeps the line of fire.
There are only two types of the customer contact centers out there. The first one is the one where the operators explain the product and teach how to use its features, the other one - constantly apologizes for the inconveniences. Talking with aggressive customers means stress and negativity, which is not easy to handle non-stop, and staff turnover in these contact centers is 120% in six months. You can train the soldiers just at the front line, but when the product is bad - there cannot be a great support.
One of my friends used to work in the support team of the online cosmetics shop, and every time she was talking about her job, she rolled her eyes saying - "Oh, poor customers! Never buy this bullshit!" That's it. This is a ship that is sinking – time to close the business without doubts.
The employees should believe in the product, defend the brand and use the product themselves. During the onboarding training, educate the employees of the values and features of the product. Once in every quarter, organize a seminar, meeting with product specialists, developers, and marketing professionals, so that the support staff know what is happening with the product and can share the customers' reviews collected at front line. If the employee is sure that the company offers a great product, he really tries to help the customer, and, as a result, the customer support acts just like additional sales department.