Chat show host Piers previously told the Leveson inquiry he listened to a voicemail message left to Heather by her former husband Sir Paul McCartney, but refused to say when or where he heard it because he wanted to protect a "source".
On Thursday Heather said she hadn't given permission to Piers, or anybody, to access her voicemails, and that she hadn't played a recording to the former editor.
"I couldn't quite believe that he would even try to insinuate, a man that has written nothing but awful things about me for years, would relish in telling the court if I had played a voicemail message to him," she said.
Heather told the inquiry that in early 2001 she and Sir Paul had argued about a trip she was planning to Gujurat, and he later left a series of messages on her voicemail.
"In the morning, when I woke up, there were many messages, but they were all saved messages which I did not quite understand, because normally they wouldn't be but I didn't think too much of it.
"There were about 25 messages all asking for forgiveness of what had happened.
"One of them said, 'please forgive me' and sang a little ditty of one of his songs on the voicemail."
She told the hearing she hadn'r recorded the messages and deleted them straight away. But she said she was then called by a former Mirror employee saying they had heard a recording of the message.
She said she threatened to take action if the story was published, and it wasn't. But in 2006, in a piece in the Daily Mail, Piers referred to having listened to the message.