Contact support via WhatsApp (available in English there), but keep in mind that Vodafone doesn’t have to accept the revoke of the cancellation.
from the bot there you repeatedly request a Kundenberater until you get forwarded to a human agent. The response can take time, this is no live chat and requests are worked on in chronological order.
https://forum.vodafone.de/t5/Vodafone-News/Dein-Kontakt-zu-Vodafone/td-p/1912292
