pH probably too way low from lemons. Test it out using litmus strips, 3.2 at absolute lowest if you wanna see fermentation. You can add calcium carbonate but you can't add too much without getting off flavors. Another idea is to just water this down more and go from there.
Don't forget that raisins need to be cut, and you need to aerate (if it wasn't done yet). If I remember correctly, a lemon mead like this probably won't be too drinkable unless you backsweeten the living hell out of it.