When I re-upload products to CRM it creates clones rather than overwriting.

When I re-upload products to CRM it creates clones rather than overwriting.

I regularly need to update product prices in bulk. I want to do this by updating products in bulk with the overwrite function on upload.This unfortunately ors not overwrite it nearly creates duplicates. This makes the system completely useless for us! Is this a bug? can it be fixed or solved?
Cheers
Dan