Depending on the type of subscription you joined, whether it's monthly or annual, your Unlimited membership will auto-renew one month/year from the date of your purchase, when your Unlimited expires.
To see the date of your Unlimited expiry, go to your Account page. Click on the 'Subscriptions' heading, under the Unlimited section you can see the date it expires.
The status of your current subscription will say "Active": to turn off your subscription auto-renewal, click on the "cancel subscription" tab. If you turn off the auto-renewal, your subscription will not renew itself on the date your membership expires and you will not be charged, unless you reactivate it.
Please note: If you have purchased an Unlimited membership before the 17th January 2022 see Renewing Unlimited