A while ago, I stopped using my old account because of drama that was going on at the time, and sometime after that, I decided to delete my Yahoo email as a way of reducing my digital footprint. Because my old account is collecting dust, I’d like to have it deleted, but I don’t know how to do that.
If you don’t have the password anymore and no other way to prove ownership, there’s not much you or we can do here unfortunately. I hope you can understand we simply cannot delete accounts by unverifiable requests.
I have the same problem. I had to start a new account with the same email address. I do know the old username and the old password, yet joindiaspora will not let me sign in. Now I am stuck with a useless account that only is called discourse and there are no contacts on it and nothing to view but the inbox. Also my sister (that lives in another country) just messaged me on the old account. I cannot see her message there because diaspora will not let me log in.
Sorry - we don’t run joindiaspora.com and can’t help you with that, at all. 
Please write an email to the administrators at incoming+feneas-association-8-issue-@git.feneas.org and ask them for help.
If they don’t get back to you soon, please let us know.
Okay thanks I will give that a try. All I get from here is an inbox I cannot use.