Either use wine conditioner (and let it sit a few days to ensure fermentation will not restart), or use sorbate and campden together, wait a few days, and then sweeten and then wait a few days.
The reason the wine conditioner (or the sorbate/campden) may not "work" is that it doesn't kill yeast, only inhibits yeast reproduction. If there are lots of yeast still in suspension in the wine, or there are a lot of lees, the yeast don't need to reproduce to restart fermentation. Stabilizing only works when the wine is clear, fermentation has stopped, and the wine is racked off of the lees.
I've had good results with using 1/2 teaspoon of sorbate and 1 campden tablet per gallon of wine, dissolved in 1/4 cup hot water. I put the solution into a new carboy and rack the wine into it. I waited a couple of days, and then sweetened the wine. I waited a couple more days (to double check and make sure it wasn't going to start fermenting) and then bottled.