Neither payment option works for me despite having a functional debit card and bank account with direct debit. Is there any way I can proceed?

Thanks for posting here in the Community, @m.macharacek. 

You can pay for a QuickBooks Online subscription using a MasterCard, Visa, AMEX or a Direct Debit card. Since you're unable to change your billing information, I've checked here on my end to see if there are ongoing investigation about this. 

Our product engineers are aware of this issue, and treated this as a high priority. They are actively working to have a permanent fix. 

I want to ensure you're updated on the progress, so I'd suggest contacting our Customer Care Team. They can add your company to the list of affected users. You'll receive email notifications once this issue is resolved. Here's how: 

1. Go to https://quickbooks.intuit.com/uk/contact/. 
2. Under the Help and support section, get the phone number for QuickBooks Online. 

To learn more about updating your credit card details, you can check out this helpful article: Update Your Card Information. 

I appreciate your patience on this matter, @m.macharacek. 

I'm always here to help if you have further concerns. Have a good one.