Find the charge first
Match the amount and date to the account, the plan and the last invoice before you reply. Check for a renewal, an added seat, usage above the plan or a trial that ended.
Explain it in one plain sentence
Say what the charge is for and what period it covers. Skip internal terms. If the customer forgot a renewal, remind them gently with the date they signed up or last renewed.
Fix real mistakes at once
If you charged twice, charged the wrong amount or ignored a cancellation, say so, refund it and apologise without hedging. Speed matters more than the wording.
Give them a choice when the charge is right
If the charge is correct but unwelcome, explain what you can do within your policy, such as a refund for a recent renewal, a downgrade or a cancellation going forward. Do not argue about whether they should have noticed.
Confirm in writing
Send the outcome with the amount, the date it will appear on their statement and any invoice. People dispute charges with the bank when they hear nothing.
Prevent the next one
Send renewal reminders, show the price clearly at checkout and tag these tickets. A cluster of the same complaint is a billing or messaging problem.