You’re best off reporting this in-app or over email to help@monzo.com
The staff will need to look into this for you, whereas us on the community are users, just like you
It sounds like you’re still using the prepaid card by your reference to the 9 digit code, is that correct? If you upgrade your Monzo account, you can set up a standing order using your new sort code and account number.
Just as @rusty said, contact support, they’ll help you out (and while we’re here, you have until April 4th to upgrade to the current account, with a unique sort code and account number).