The buyer's comment was that they had "informed you that they would withdraw from the purchase". This suggests they didn't understand you had cancelled the sale. There are two possibilities to get the feedback changed.
The first is that you didn't cancel it properly. You can't just tell buyers that a sale is cancelled, and it won't have been unless you followed one of eBay's two procedures for cancelling. If it isn't cancelled properly this would explain the buyer's comment, as eBay will still be sending them payment reminders. This would be good for you, as if so you can now cancel the sale properly for non-payment, see: https://community.ebay.co.uk/t5/Announcements/New-cancel-function-for-unpaid-items/ba-p/6939127 If you can still use this procedure, and the buyer doesn't pay, the sale will be cancelled, your selling fee returned and the feedback left will automatically be removed (if it isn't, you can ask eBay to remove it).
If you did cancel it correctly, but through the ordinary cancellation request procedure, your only other option would be to explain this to the buyer (use Google translate if necessary). If you can resolve the problem and restore good relations with the buyer you can send them a request to revise their feedback: https://www.ebay.com/help/selling/leaving-feedback-buyers/disputing-feedback-received?id=4102#sectio... You would have to send the request within 30 days of receiving the feedback, and the buyer will have 10 days to revise it.
