Why can't I use my data contracts form my IService?

Question

I have the following data contracts defined in my IService:

[DataContract]
public class PumpClass {
    [DataMember]
    public int ID { get; set; }
    [DataMember]
    public double litresPumped { get; set; }
    [DataMember]
    public double price { get; set; }
    [DataMember]
    public string fuelType { get; set; }
    [DataMember]
    public DateTime date { get; set; }
    [DataMember]
    public bool requestUse { get; set; }
    [DataMember]
    public bool requestAccepted { get; set; }
    [DataMember]
    public bool finished { get; set; }
}

[DataContract]
public class DieselTank {
    [DataMember]
    public double MaximumLevel { get; set; }
    [DataMember]
    public double WarningLevel { get; set; }
    [DataMember]
    public double CurrentLevel { get; set; }
    [DataMember]
    public bool OrderFuel { get; set; }
}

[DataContract]
public class UnleadedTank {
    [DataMember]
    public double MaximumLevel { get; set; }
    [DataMember]
    public double WarningLevel { get; set; }
    [DataMember]
    public double CurrentLevel { get; set; }
    [DataMember]
    public bool OrderFuel { get; set; }
}

[DataContract]
public class CostOfFuel {
    [DataMember]
    public double DieselSupplierPrice { get; set; }
    [DataMember]
    public double DieselPrice { get; set; }
    [DataMember]
    public double UnleadedSupplierPrice { get; set; }
    [DataMember]
    public double UnleadedPrice { get; set; }
}

[DataContract]
public class Sale {
    [DataMember]
    public double value { get; set; }
    [DataMember]
    public double volumeSold { get; set; }
    [DataMember]
    public DateTime dateSold { get; set; }
}

[DataContract]
public class Ordered {
    [DataMember]
    public double volume { get; set; }
    [DataMember]
    public double cost { get; set; }
}

but only PumpClass, DieselTank and UnleadedTank can be seen from my service that uses this interface and I don't know why. Only these 3 show up in the data sources for Visual Studio as well.