x10 provides some free subdomains. .x10.mx has been the standby for years, but there are many others like .pcriot.com. These don't have a fee associated with them.
Scam alert! Please read this carefully!
I have gotten many scam emails suggesting that I have to pay for domain registration, or something about losing my domain because someone else is buying it, or needing to upgrade my account to get higher rankings in google searches. These are all scams.
Firstly, make sure it's a domain you own. Scammers will try to sell you a virtually worthless yoursite.something if you own yoursite.example . If the email is about a similar, but not the same domain, it's a scam (or at least a sales pitch you can ignore)
Secondly, make sure it's your registrar. There are a million registrars out there, and x10 is one of them (https://clients.x10premium.com is where you log in). As always, don't click links in emails. Go straight to their website.
Thirdly, please find a registrar that offers a privacy feature to hide your personal details. This is often free with any good registrar. This prevents spam and snail mail offers to sell you stuff. I get phone calls all the time about designing a website because I made this mistake.
If you would like to provide your website address here, we can provide more information. Your registrar can be found using a WHOIS service.