The best way to find this out is to see if you're the Registrant on a public "Whois" lookup for the domain. Either use your web browser to search for a "Whois Lookup" and use one of the listed websites to search for your domain, or open up the command line from your local machine and enter the command: whois domain.com
You then need to find the section labelled registrant ID, if your name and details are listed there, you are the named registrant.
If you are not listed here, but believe you are the rightful owner, please contact the registrar (also listed) for more information. Disputes over domain ownership are often handled by the top-level authority, but the registrar should be the first point of call.
It's always worth keeping your domain contact information up to date to help avoid any confusion. If your plan on changing and details, for example your address or postcode, or perhaps your now using a new email account - you should let your registrar know in advance. Some domains have strict verification rules in regards to keeping information up to date, if the rules are not adhered to, this can result in your domain being taken offline.