There could be various ways to counter any defamatory content. You will have to come up with the right evidence and you will have to tell the author that the statement generated is not based on the facts. You will have to provide complete evidence of the case and you will have to provide correct information about the scenario so they can change their statement.
If it all fails and the author rejects your request to remove the content, then you can request the hosting company and provide them with complete evidence of the case.