Sometimes, during migration (or any other massive upload process), it's possible to accidentally issue multiple re-uploads requests for the same image due to a bug in the code.
Cloudinary Uploader's default behaviour is to allow overwriting of any existing resource in the case of a names collision. Therefore such re-uploads will succeed and result in an increased consumption of Monthly Transformations.
It's strongly advised to have good monitoring on your uploads and to be alerted to such exaggerated activity. This will allow you to take actions and prevent unnecessary plan upgrades and additional costs.