Those values are great for current limiting in LEDs or so. Not for signals. Your encoder won't be happy having to supply 13 * (12 / (47 + 68)) = 1.4A of total current on its outputs (at 12V those voltage dividers conduct 104 mA each!). Those resistors are also bound to get pretty hot, as you ask them to dissipate 0.3W resp. 0.4W.
47k and 68k will work a lot better. This way you're going to destroy your encoder (if you haven't done so already - it would explain why you get the same output all the time). In fact, if your resistors don't start smoking (I assume you're using standard 0.25W ones) you almost certainly destroyed your encoder already.