Name and message of SEPA really important?

I’m also confused…

How does this scam really work ?
If the scammer has the ability to make a SEPA transfer (directly through controlling the victims computer, or indirectly through some kind of social engineering trick) he probably has the ability to write whatever he wants in the message field.
He can’t change the name of the account holder of course, but why would he want to ?

Also, what really happens in such a situation ?
They freeze my account and I have to use cash for a week until things get sorted out ?
Or could it be worse ?