scscope find c foo
does what it's supposed to do: display a list of functions calling foo
in the command line and open the chosen one in an horizontal split.
But that is not what you want, is it?
The list of possible targets is always displayed in the command line which is expanded as needed: it can't be displayed in a window at all.
That said, you can use the quickfix window to display the list instead of the command line, see :help cscope-options
.