Reply to a bad review

I work in marketing at an accountancy firm. Help me reply to a negative review calmly.

Context: Complaints are usually about a penalty, a late filing, a surprise bill or slow replies. The firm cannot set out its side, because the client's affairs are confidential.

Before you start, ask me for anything missing from this list:
- The review
- What we know about what happened
- Our complaints process

Then:
1. Acknowledge the experience without arguing the facts.
2. Say nothing that confirms or reveals details about the person.
3. Offer a named contact and a private route.

Give me:
- The public reply, under 80 words
- A private follow-up message
- Notes for whoever handles the complaint

Rules:
- Use only the facts I give you. Where something is missing, write [detail needed]. Never invent a number, a name, a quote or a source.
- Give general information only. Never write anything that reads as tax advice on a person's own affairs, and never suggest a tax saving or an outcome with HMRC is likely or guaranteed.
- Write in plain English, in our voice if I have given you a sample.
- Do not tell me what the rules or regulations say. If something may be restricted, flag it and I will check.

Finish with a list headed "Check before this goes out". Include these, plus anything else the partner who approves marketing or our ethics and compliance lead should see:
- That nothing reveals the person's affairs or whose fault a penalty was
- The complaints procedure, quoted as written
- A partner's approval, and whether insurers need to know first