It seems that TeamViewer keeps my account active even if I haven't paid their bill.
I also cannot submit a ticket for closing this (the support portal loads the Community)
https://community.teamviewer.com/English/kb/articles/72027-how-to-submit-a-ticket#toc-hId--440241381
How on earth am I supposed to cancel this account once and for good?
Hi there - not paying the bill does not cancel a subscription. You need to submit a ticket for this. For submitting a ticket, you need an active license on your account. In case, your license is not working at the moment due to the outstanding bill, I suggest calling TeamViewer and ask them for help in submitting the ticket.
Thanks for your understanding that such license and contract related topics can´t be resolved within the community.