Apparently, you have received a partial order. This is either because the other part of your order has become permanently unavailable or because it is delayed and will be sent later.
Partial orders incur no additional delivery costs to you. You will only be billed for what you receive. We sometimes decide on partial orders as a free service to our customers, when the complete order would otherwise be unduly delayed.
You can check your order status online to verify exactly what happened.