"It's a lie started thirty years after Darwin's death by a creationist looking to advance a political agenda."
From what I've read he (Darwin) recanted it just before he died.
Those are "weasel words." "From what (you've) read?" Kindly cite your source.
That claim has been refuted by historians. It's also been debunked by plenty of creationists. The lie was started by a woman thirty years after he died, who suddenly started telling this story of a visit that she made to him before he died three decades previously. She never mentioned it at all before then, and she had no proof that she ever visited him in the first place.
Even "Answers in Genesis" admits that it's not true. You have been told, you have been shown proof (from your own side!) that it's not true. If you continue to spread this fiction, you will be doing so with the full knowledge that it is a lie.