On the Technic Launcher choose Options, select "Manual Build Selection", then choose "3.1.1 | 1.2.5 | Latest" from the drop-down menu. Once that's done login and try to join a 3.1.1 server.
If you have already done all of the steps above, I would recommend to delete your tekkit folder entirely (make sure you backup your worlds) and restart the Technic Launcher.