Taken ages but I've managed to figure this out, answer below in case anyone has the same problem.
//Remove unwanted series
EnquiriesChart.Series.RemoveAt(0);
//Set chart properties
EnquiriesChart.ChartTitle.TextBlock.Text = "Enquiries " + YearDDL.SelectedItem.Value;
EnquiriesChart.Width = 914;
EnquiriesChart.PlotArea.XAxis.AxisLabel.TextBlock.Text = "Months";
EnquiriesChart.PlotArea.XAxis.AxisLabel.TextBlock.Appearance.TextProperties.Color = System.Drawing.ColorTranslator.FromHtml("#666666");
EnquiriesChart.PlotArea.XAxis.AxisLabel.Visible = true;
EnquiriesChart.PlotArea.EmptySeriesMessage.TextBlock.Text = "No data for the year selected.";
//Set X-Axis to show months
EnquiriesChart.PlotArea.XAxis.AutoScale = false;
EnquiriesChart.PlotArea.XAxis.AddRange(1, 12, 1);
EnquiriesChart.PlotArea.XAxis[0].TextBlock.Text = "Jan";
EnquiriesChart.PlotArea.XAxis[1].TextBlock.Text = "Feb";
EnquiriesChart.PlotArea.XAxis[2].TextBlock.Text = "Mar";
EnquiriesChart.PlotArea.XAxis[3].TextBlock.Text = "Apr";
EnquiriesChart.PlotArea.XAxis[4].TextBlock.Text = "May";
EnquiriesChart.PlotArea.XAxis[5].TextBlock.Text = "Jun";
EnquiriesChart.PlotArea.XAxis[6].TextBlock.Text = "Jul";
EnquiriesChart.PlotArea.XAxis[7].TextBlock.Text = "Aug";
EnquiriesChart.PlotArea.XAxis[8].TextBlock.Text = "Sep";
EnquiriesChart.PlotArea.XAxis[9].TextBlock.Text = "Oct";
EnquiriesChart.PlotArea.XAxis[10].TextBlock.Text = "Nov";
EnquiriesChart.PlotArea.XAxis[11].TextBlock.Text = "Dec";
//Set Y-Axis scale
EnquiriesChart.PlotArea.YAxis.AutoScale = false;
EnquiriesChart.PlotArea.YAxis.MinValue = 0;
EnquiriesChart.PlotArea.YAxis.MaxValue = 50;
EnquiriesChart.PlotArea.YAxis.Step = 5;