It does not become fully clear from the code snippet what might be causing the issue. I attached a sample project(PieChartSample.zip) using LabelSettings to help you start with.
I would also suggest in case you are just starting with the chart, to to take a look at our newer charting control - ChartView
and consider using it over the older one.
Moreover you will find attached a sample with the newer chart control ChartVIew_PieChartSeriesDemo.zip)
Hope this helps.
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