Can I Not Just 'Reset' My Dropbox or Otherwise Delete Every File in it?

My Dropbox is a cluster. So I bought two external drives and downloaded all my files to one drive and then copied that drive to a second drive (in case the first fails at some point).

Now, how in the heck do I delete all the files on my Dropbox? I have a paid plan and I just want it set back to zero. I'm on the verge of simply canceling it and moving on with a different cloud service. 

Seems like I'm down to two folders left. I guess that are both prior sync'd folders to previous computers. It's like 700GB so I need it gone. But it won't let me simply delete the files. I get in a hamster wheel of it telling me [pop up] "Delete Desktop from your My Mac backup? Go to back up settings to delete desktop. If you no longer have access to the computer, you use to create my Mac backup, click, I don't have access." So, I click "I don't have access." Then it wants me to click "settings" to "unlink" My Mac and under Security Tab sign out. But under the security tab and Devices the Mc Mac isn't listed. So, now what do I do? There is another folder called My iMac (haven't had an iMac in Years). I cant get rid of those files either.

Any ideas?

Why can I not just reset my account THAT I'M PAYING $199/yr FOR?!!!!?  I'd seriously just cancel the whole thing now, but it doesn't renew till next February.