Those yeasty beasties

Forgive me, it’s my first time making mead. I racked my strawberry pie mead from its primary into the secondary and added more strawberries and vanilla pod. It started fermenting again, overflowed the airlock. 🙄 okay, switched to a blow off system. My question is, how do I stop the yeast? It’s already sitting at about 16-18% abv and is unbelievably dry. I want to start forming the strawberry pie flavor to be more present and backsweeten without the yeast continuing to ferment. Any ideas on how to do that and/or work on the flavor?