I am getting unreal IP from DuckDNS and "where is my IP address" websites

I haven’t been able to connect to my Home Assistant through the Duck DNS domain for a few days. The problem is that the public IP changes every time a request is made. If I look at https://whatismyipaddress.com it gives me one IP address, if I look at https://www.iplocation.net/ another… Duck DNS’s IP is constantly changing and it gets an unreal IP. If I check the router if I get the real IP. I set it to Duck DNS and the connection works… until the IP is reloaded again (2 minutes). What I can do?