The below can be the possible reasons:
1. Your payment has become overdue.
2. Your account has been deleted because of non-payment. The accounts are deleted in case the payments are not received even after 15 days of due date.
3. There could be server related issues from our end. In this case our team is already on the job to fix the issue. Please try to login after some time. In case the issue persists, contact the support.