With a beer that strong, you probably should have repitched at bottling. There are several factors that the yeast must fight in this situation, including:
- high alcohol strength - almost 10% ABV
- cool temperature - the bottom two degrees of the yeast's fermentation range
- long settling time - six weeks
There's good news, though. That strain should be able to tolerate alcohol around 12%, and that strain has low-medium flocculation, so there should be enough viable yeast in your bottles to repopulate and consume the priming sugar. It will just take some time for the yeast to work in such a harsh environment.
I always see slow carbonation times when I bottle condition with such strong beers. Four weeks is not uncommon, and that's at 68°F.
Leave your beer at 70°F and check a bottle weekly - and wait two weeks on the first bottle if you can afford it, since it will need as much time as you can give it.
I would be surprised if the brew didn't carbonate in another 3-4 weeks, but should that be the case, you may have to pour them back into a carboy and repitch yeast (a more robust strain like champagne yeast) before rebottling.