These are the tasks we need to do:
For each user, determine their country based on the IP address
Fail on the first step. No point of going any further.
Almost every browser nowadays offers inbuilt VPN to prevent you from being traced. Some mobile browsers have this option by default.
With this option activated you'll always see the IP of the VPN host, not of the actual ISP of the customer.
Any assumptions based on the false source data will be wrong.