I am going to assume that your name 'In the know' is ironic.

Interest can be charged daily, hourly, monthly or in fact at any interval of time. However if you have an annual APR of 60% this absolutley does not mean that you will be charged 60% each month!

This issue sounds liek a classic example of nobody in the organisation knowing how Interenst is calculatd on a loan and indeed the generally poor standards of maths we have in these organisations that they couldn't even spot very large accounting errors.

I am afraid that FOS is probably the only cause now as Welcome seem unable and unwilling to resolve the issue.

Please let us know how you get on