Premium and Enterprise plans (monthly & annual) renew automatically on the anniversary of the day you subscribe.
If you want to stop your account from auto-renewing, all you need to do is cancel your subscription. You can do that here: https://my.sonix.ai/account. This will stop you from being charged a subscription fee.
Note that when you cancel your subscription you lose access to your files.
You can however, purchase a storage plan to maintain access. The storage plan is $5.00 per month per 50GB. If, at some point in the future you want to re-subscribe to Sonix, you can easily do that on your account page: https://my.sonix.ai/account