Why not consider unlocking that account instead of requesting its deletion? Given the account's age, there might be some value in doing so.
I'm not sure about the exact requirements and what needs to be done, but have you tried sending an email to the provided address?
Unlocking the old account does not solve the main problem, namely that this thread is attached to the current account, which was created many years ago and which has value (and is also well indexed by search engines). Assuming that you use the old account to communicate with users, while maintaining the thread, then this also does not solve problems. The reason is that if the team will communicate with us on behalf of "eXCh", then most users will still be confused, because when they enter the thread, they will first see the account that created this thread, the account named "eXCh.cc".