Announce it before the first ticket
Tell customers in advance by email, with the new price, the date and the reason. Most angry tickets come from people who found out on the invoice.
Write the main reply once
Prepare a saved reply that states the new price, what changed and where to see the plan. Agents edit the first line to answer the person's specific question.
Decide grandfathering up front
Choose whether existing customers keep the old price for a period, and say so. Making this up per ticket looks unfair and causes more tickets.
Offer options before discounts
Point out a cheaper plan, an annual price or fewer seats before reaching for a discount. A reflex discount teaches customers to complain.
Handle cancellations kindly
If someone leaves, make it easy, confirm the end date and ask one question about why. Keep the door open without pushing.
Watch the numbers for a month
Count tickets, cancellations and plan changes by day. Use what you see to adjust the wording, not the price, unless the data says otherwise.