I agree with Gil, a little warmer will help...I bottle carb in my basement which is usually running around 66*F and they take a good month and a half.
The other option that hasn't been considered is if your bottle capper is working properly. If it caps your bottles but leaves a little leak, they wouldn't be contaminated (just like if you put celephane and a rubber band over the fermenter) but they wouldn't be carbed either because the CO2 was escaping.
You could try putting some ginger ale in an empty bottle, capping it and shaking the bottle to eliminate this possibillity. If you end up with Ginger ale all over you...well...get a new capper.
I have a feeling it's the temp being to low, though...take them out, give them a good swirl upsidown to make sure the sugar and yeast are all in suspention, and set them in a corner of a room you know is closer to 21*C, give it four weeks and check again....