At 6.5% alcohol, new yeast *might* help, but you'll want to use a starter so it's active and add some nutrient so it will continue in the beer.
Belgian strains can stall out if they get too cold. And, their version of cold would be a sweat box for most ale yeasts. With the majority of fermentation past, raising the temperature to 80oF would be fine. Although this isn't related to you, there's a couple of Saison strains that don't seem to dry out the beer until nearly 90oF. So, it's really about giving the yeast what it wants and not making assumptions for it.