Rewritten epistle torn open — you won't like what it says! (6-3,6)

I believe the answer is:

poison-pen letter

'you won't like what it says' is the definition.
(an abusive letter)

'rewritten epistle torn open' is the wordplay.
'rewritten' indicates anagramming the letters.
'epistle'+'torn'+'open'='epistletornopen'
'epistletornopen' is an anagram of 'POISON-PEN LETTER'.

I've seen this clue in The Times.

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