Try to check your client IP ether the addr with any IP addr checker like https://api.datascrape.tech/latest/ip or https://www.cloudflare.com/cdn-cgi/trace with and without proxy - the IP should be different. This way you will find out, whether the proxy is used or not.

If the proxy is used and you still limited by target WEB site - pay attention on your fingerprint like SSL fingerprints and TCP fingerprints. You can test them and find more info here https://datascrape.tech/tools/browser-leaks-test/