How can I deactivate an old Dropbox account, without access to the email?

I have an old Dropbox account from the high school, which was registered to my school email address. I keep getting emails and pop-ups on my laptop from that account and I'm sick of seeing it, especially since I never used it and want nothing to do with anything from my old high school. since it's been years since I've been in high school, that email has been deactivated and I do not remember the password for this account since I never used it. It's because of this that I am unable to figure out how to deactivate the account, and because I'm not a "subscriber," the "customer support" won't let me speak to an actual person to get this figured out.