Not sure what ipleak website uses but consider clients/browsers/cookies of sorts can collect various bits of data on you and relate this to your location. Mind your clients and other protocols for identifiable information.
Some browsers share your location- look out for that permission (usually at top of browser). Some save location for future websites.
Another example being DNS server leaking can give away your location even if the connection itself is proxied (some ISP’s assign local DNS servers).
TBH not easy to guess your exact problem based on the small, extremely vague information provided on your setup/usage of internet…