Tile Hero Not Letting Me Use My Gems

I've been frustrated that I purchased gems so I can work through the harder games of Tile Hero. When I've run out of lives or want to add helps, I'm always sent to the Gems Store. I'm stuck on level 334. Why won't the game let me use my gems? What is wrong here!? Can I get a refund of my purchase price for my useless gems?

Sonia -- on Windows PC