Pivot Chart Date Grouping

This is my first post and I am looking for help.

I have a spreadsheet of invoices, with invoice number, invoice amount, and date. I need a combo chart with column show invoice amount total for each month, and a line chart showing running total.

I am already create a chart, the problem is I can't show the Horizontal Axis (Date) as Month. If I group them and show by month and year as I want, the running total reset every year. If I don't group, the running total is fine but the date are all the specific date of invoice. I tried to change the date format to show only month, but since I have multiple invoice each month, it will show multiple month and more confusing.

What I am looking for is, group the pivot chart by month and year, for example it could show from May 2017 to Sep 2018 in sequence, but the running total do not reset to zero on Jan 2018.

Thank you for your help. Any suggestion is welcome.

Thanks a lot.