[Defender Pro] Suspicious File Wont Delete

I recently installed defender on my site – cheseldineautogroup.com and it found a suspicious file. I tried to delete it through the defender dashboard but it would not delete. I also tried to go onto the cpanel and delete and it still won't delete. Can you advise me of what I should do next. I also noticed this same file in another account. I'm sure it must be a hack. Thanks