Dropbox Salesforce application owner

Hello all,

today at our company we run into a problem i will try to explain the best way possible.

in 2014 some developer integrated with our Salesforce a dropbox console app.

today we tried to create a new user which throw an error saying we reached the maximum users.

now the point is that we want to upgrade the account(used to create the app for integration) which owns the application but we cant find/lost the email used to to register the app, or even if the account was deleted but somehow the application is still running.

we only have the key and private key used for the integration.

how can we solve this?

thank you!