When I configured community on my Org I removed System Admin (me) profile from Community Members (see the screenshot 1)
So neither System Admin not anybody else can manage, modify or delete this community
How to get access to community back?
Below the link how to add system admin (yourself) to community to be able to manage it.
Hi Try to get in touch with salesforce support team. They are the omnly one seems like will be able to help.
call them on 1 (800) 667-6389 here is there number. or contact them through email on using this link https://www.salesforce.com/form/contact/contactme.jsp