There are publicly available "Whois" look-up functions which can tell you what organization you registered a domain name with and who you need to continue paying the annual renewal fee to. (You can optionally renew for multiple years if available.)

For example, you can use the https://whois.com/whois form. Enter your domain name and it will display a list of publicly available information about the registration of that domain name including the owner and contacts for the domain name -- unless that data has been redacted for privacy purposes or to reduce the incessant spamming that happens to any public email addresses in the Whois database.

On the output page, you are looking for the line which begins "Registrar: ...". However, some registrars, like Tucows Domains as an example, are wholesale providers of domain name registration services to resellers. If you have a question about your domain name, or want to have a change made to any of the details stored on your domain name, you will be unable to contact a wholesale provider (since you aren't their direct customer). Instead, you need to find a second line on the output page. This second line begins with "Reseller: ..." and it might be found further down the page, perhaps in the section called "Raw Whois Data". In other words, if the Reseller line exists, then reach out to this company for support. If the Reseller line does not exist, then reach out to the Registrar company for support.

If Tucows Domains (wholesaler) is the Registrar, and if the Reseller line cannot be found (sometimes it's suppressed if the reseller has not populated their profile), you can enter your domain name into Tucows' reseller look-up form to find your "Domain Provider" at https://tucowsdomains.com/provider-search/