Is it possible to write "Thank you for your soon answer" in a letter?

thanks Emotion: smile
No, one would not say, "soon response."

A better way to express what you are trying to relate is, "Thank you for your prompt response." or, "Thank you for your prompt reply."
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I should have explained that soon is an adverb and you need an adjective to modify the noun response. You could use quick, immediate, prompt, rapid, etc.
Thank you for your prompt response. sorry for the wrong attachmenti have re send right one please check with your bank i think it credited to your account. because from our account money all ready debitedso kindly cross check with your bank with attachment slip

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