你的内容已经表达得很清楚了，但可以稍作修改以更自然和正式。以下是修正后的版本：
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Subject: Request for Information Regarding CD-Key Activation
Dear Steam Customer Service,
I purchased a CD-Key from a third-party platform. When I attempted to activate it, I received a message stating that the key had already been activated by another Steam account. The platform has informed me that they will only issue a refund if I provide a screenshot showing when the key was activated.
Could you please provide me with the activation details of this CD-Key, including the date it was activated and, if possible, the account to which it was bound?
Thank you very much for your assistance.
Best regards,
[A Steam User]
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修改说明：
1. 标题：添加了明确的邮件主题，便于客服快速了解你的需求。
2. 更清晰的表达：
o "bought a CD-Key on a platform" → "purchased a CD-Key from a third-party platform"（更正式且明确）。
o "it is said" → "I received a message stating"（更自然）。
3. 更礼貌的请求：
o 使用 "Could you please" 代替 "I hope you could"，更符合正式请求的语气。
4. 细节补充：
o 明确说明需要的信息（activation details, date, account）。
5. 结尾：
o "With friendly regards" → "Best regards"（更通用且正式）。
这样修改后，邮件会更专业、清晰，也更容易得到客服的积极回应。
