Server firewall can block ip for any specific reason like multiple wrong attempts to access cpanel, malicious / harmful activities or, any other things that may seem unusual. If firewall blocked your IP you can’t visit your cPanel url & hosted website.
So, your first task is to find your IP. visit this link https://www.whatismyip.com and copy your IP Address from these site. now, if you are a VPS / Dedicated user login to your WHM -> ConfigServer Firewall -> Unblock IP.
If you are a shared hosting user you can unblock from here,