how to 'flush hosts' via ssh
What "users" exist in MySQL?  I hope you are not doing everything as root (or other SUPER user)!

Once you get past this problem, be sure to have a user that will let you get in, but is not being used otherwise for the application.

What I just said is good advice, but it may not be relevant to your symptom.  It seems that your host (at IP xxx.xxx.xxx.xxx) has been pounding on the shared account.  Could this be?  Could it be that a hacker got into your host, and is using it to get at the hosted MySQL?

Is there another machine from which you could try to do the FLUSH HOSTS?