I've had this happen too quite often. 

Try changing the password too.  Even though it suspends the account it seems to hold open the SMTP session or remember its state. At least this way the next time it tries to establish it'll get a wrong password and get locked out.   I have no clue why but I saw a big discussion on this years ago here.  I could probably be wrong but I tend to go to the extreme when there is a compromised account.  There is a root problem with the customer account so I'm disabling it entirely until they are notified to clear up their mess.  I've gone as far as blocking the IPs in the firewall as well. 

I've also sometimes seen that it wouldn't stop sending until you completely rebooted the system.  Shutting down surgemail and starting it back up didn't fix it in many cases.   I never did see what the resolution was. 

From: "Tom Cross" <HIDDEN@tml.com.au>
To: surgemailHIDDEN@etwinsite.com
Sent: Wednesday, April 15, 2015 4:03:58 AM
Subject: [SurgeMail List] Suspended account still sending mail