Visit www.bookbeat.com and log in to your account. Once logged in, click on the button "Reactive my account" and your account is reactivated. You might need to fill in your credit card details again.
If your payment details are no longer valid, you might have to update them before you can reactivate your subscription. To do so, click on "change" next to your payment method. Enter your new information and press "Save." Finally, press "Activate" again.