Well, I do not know how you stop auto-vacation, but I think this might help your problem. Try pressing the "Account" button under the "My Home" tab at the top of the page. Then, try going under your Online Chess Settings on the Account page. At the bottom of the Online Chess settings page, there should be a check box that says something like, "Pause My Games!" If the check box is marked, then unmark it and "Save your Changes." If that does not help, then follow this link and read all of the FAQ:
http://support.chess.com/Knowledgebase/Article/View/26/0/how-does-vacation-work--how-much-time-do-i-get
If that doesn't work either, then just contact the Chess.com Help and Support. If you need the link to Contact Support, just ask because I will be tracking this forum topic.
-BlueGator456
-I hope I can help!
How do you stop chess.com from automatically placing you on vacation when your time runs low?