The phone number (in my opinion) is not a great way to contact Monzo. You’re better off using the in app chat, contacting support, and waiting patiently for a response (they will get back to you).
@redshift gave directions above on how to do this
If you can’t see “I can’t find what I’m looking for”, then you can also search “contact support” and that will bring it up to.
I know it can seem stressful if you can’t move your money but at least you know it’s not going anywhere and it will probably really easy to sort out.
This is primarily a customer forum so we can offer suggestions but we can’t actually help ourselves.