Thank them without defending
Thank them for the feedback and do not argue. They have already decided and are telling you what they think.
Find the real reason
Ask one open question if the reason is unclear. Price, a missing feature, a bad support experience and a business change need different follow-ups.
Fix what you can fix
If it is a bug or a misunderstanding, say what you will do about it. Do not promise a feature that is not planned.
Record the reason
Tag the ticket with the reason and count them monthly. A rising tag is a product or pricing signal.
Leave the door open
Tell them how to return and keep their data as your policy allows. Do not chase them with repeated offers.