Example:
To whom it may concern:

I have not received the order (# xxxx) that was shipped on xx/xx/2006. It has been over 8 weeks (put any time) since its dispatch. I want to request a refund to my credit card.

Regards,

XXXX
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如果要加強語氣 (雖然我不認為他們會在意 )
If you still do not response to this request in few days, I will file a complaint via Canadian Consumer Information Gateaway and to my credit card company to request a chargeback.
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你最好問問你的銀行可不可以chargeback
如果可以的話 -- very unlikely -- 告訴我 我要轉過去