Updating Hebrew text in SQL Server database end up with "???"

I'm writing a C# program to enter data into SQL Server 2008 database.

I use the following function to enter info into database

public bool AddSupplier(string name, string contactPerson, string telephone, string fax, string type, string payment, string comments)
{
        _cmd.CommandText =
            "INSERT INTO suppliers (name,contactPerson,telephone,fax,type,payment,active,comments) VALUES (@name,@contactPerson,@telephone,@fax,@type,@payment,@active,@comments);";
        _cmd.Parameters.Clear();
        _cmd.Parameters.AddWithValue("@name", name);
        _cmd.Parameters.AddWithValue("@contactPerson", contactPerson);
        _cmd.Parameters.AddWithValue("@telephone", telephone);
        _cmd.Parameters.AddWithValue("@fax", fax);
        _cmd.Parameters.AddWithValue("@type", type);
        _cmd.Parameters.AddWithValue("@payment", payment);
        _cmd.Parameters.AddWithValue("@active", 1);
        _cmd.Parameters.AddWithValue("@comments", comments);
        _con.Open(); 
        _cmd.ExecuteNonQuery(); 
        _con.Close();
        return true; 
    }

This works fine, I can add info in Hebrew and it shows up in the database.

When I try to edit it using this function

public bool EditSupplier(int supplierId,string name, string contactPerson, string telephone, string fax, string type, string payment, string comments)
{
        _cmd.CommandText = "UPDATE suppliers SET name='" + name + "' ,contactPerson='" + contactPerson + "',telephone='" + telephone +
                           "',fax='" + fax + "',type='" + type + "',payment='" + payment + "',comments='" + comments +
                           "' WHERE supplierId =" + supplierId + ";";
        _con.Open(); 
        _cmd.ExecuteNonQuery();
        _con.Close();
        return true; 
}

I end up with ??? instead of the Hebrew input