Necklace of Elemental Augmentation

My tav is a level 11 sorcerer/level 1 cleric. I took my first level in sorcerer to gain proficiency with Constitution saving throws. I'm equipped with the Necklace of Elemental Augmentation. When I roll for damage, it's supposed to add 5 damage (my Charisma modifier), but it only adds +1 (I have 12 Wisdom) because it uses the spellcasting ability of the last class added to my character (so, the cleric, Wisdom). This is very annoying because I use my cantrips a lot with deduplication thanks to metamagic. So I'm losing 8 damage points per turn. Does anyone know how to make the necklace still use Charisma for the damage bonus?

https://preview.redd.it/q7rtrw6dh7dg1.png?width=1819&format=png&auto=webp&s=972443e34cbfcc5fd0ef611af06151ce2784fc52