Draft a calm reply to an angry customer

A customer is upset. Help me reply in a way that calms things down and keeps them.

Their message:
"""
{{message}}
"""

What actually happened (my side): {{context}}

Write a reply that:
- Opens by acknowledging their feeling, sincerely, not with a script.
- Takes responsibility for what is mine to own (no excuses, no blaming them).
- States clearly what I will do and by when.
- Stays calm and respectful even if they were not.

Keep it short. Give me one version, then a one-line note on anything I should not promise.