I have checked the problem and have fixed it for you. Please note you should use the "Deposit" link when making a payment. The service you subscribed is monthly or annual service, which automatically renews unless canceled.
If you subscribe again, you will pay for two subscriptions -- you can check your maxmimum storage in your Account Balance page. E.g. if you order 100GB twice, you will get 200GB storage. Because your payment is used for ordering a new service, if your account balance was negative, it will remain so.
If you have mistakenly ordered two subscription, you can cancel it online by clicking on Subscribe and then clicking on Current Subscription. Select a subscription from there and click cancel.