If you have already paid for a subscription, you can't deactivate it. You can temporarily suspend your subscription or disable its auto-renewal. For more information, go to Suspend or disable subscription.
If you disable subscription auto-renewal before the trial period ends, the subscription fee won't be debited from your card. But if you want to bring your subscription back, you won't be able to activate the free trial period again. You will have to pay for the subscription.
If you purchased your subscription through a mobile carrier, you can disable its auto-renewal in your personal account, using the USSD command, or through your carrier's mobile app. For more information, see the Yandex Plus Help.