likewise, if all your work is original - perhaps someone stole your content, and is submitting it as 'their' own...
in which case I would ask them about that. easy to prove, etc.
I do not upload the work of other authors. If what you write happens, they should block the author who uploads the video a second time.
If you want a quick response, send message on Shuttertstock Twitter account in public, facebook, IG or other. They are more likely to respond there, since it's public and everyone can see whats going on, more pressure I think to respond