If you are on a Premium or Enterprise Plan, when you cancel you subscription you will have access to all your files indefinitely. They are your files. You will always have access.
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.
Remember, no matter what plan you are on, you will always have access to your files.