Email: owning the problem
EmailSubject: Re: [their subject line]
Hi [Customer name],
You're right to be frustrated. You [what went wrong, in their terms: were charged twice, lost a day of work, waited a week for an answer], and that shouldn't have happened.
Here's what I've done so far: [concrete action already taken].
Here's what happens next: [next step], and I'll update you by [date or time] even if I don't have the full answer yet.
I'm handling this personally, so you can reply directly to me instead of starting over with someone new.
[Agent name]