Cotes De Blancs wants to finish your cider dry, usually at .990 or so. I usually let everything finish up before backsweetening, so I don't have much good advice except to point out that stopping an active fermentation with wine yeast isn't easy as you've found out. The cold temperatures might help, but once it warms up it'll probably restart. I know some people have sucessfully stopped fermentation by cold crashing and racking, so it's possible. I've never been able to do it, though.
There are threads on pasteurizing, making sweet ciders, etc so I'll let someone else speak to that. Wine choice plays a big part, though, and choosing an attenuative wine yeast means that it'll be hard to stop.