I managed to fix this myself(!!!)
I went into the style.css file (of child theme)
On line 180 where it says .header-image
Here I changed the padding to say 0 0 0
And changed the dimentions of the imapge from (something like) 1084px (or some large number) to 0.
And it magically disappeared.
Excellent.
I hope it never comes back.