First of all, I want to apologize for the apparently negative experience you had.
Can you help me improve?
Secondly, I want to keep improving and would greatly appreciate your feedback. Can you please take the time to fill out this form?
If you're not happy with anything you purchased from me, I don't want your money.
So if you'd like to get a refund, please do not hesitate to reach out to firstname.lastname@example.org