Q: I no longer have an iphone but I am still being charged for the icloud storage upgrade. Why?

Why: because if they automatically closed it and deleted the data, some people would be very upset and rightfully so. iCloud can be accessed from multiple types of devices so just resetting a device isn't enough to let them know.

How: use the following instructions to reduce to the free 5GB level: iCloud storage upgrades and downgrades - Apple Support

If you want to delete data, the following has instructions: Manage your iCloud storage - Apple Support