Hi again Lucas.

This is the default behavior of Highcharts - it sees this as Giga, and that's why "G" is there.

In order to change this, you need to add this script to the page where the chart is:

<script type="text/javascript">
jQuery(window).on('load', function(){
    Highcharts.setOptions({
                lang: {
                    numericSymbols:["k", "M", "B", "T", "P", "E"]
                }
            });
});
</script>

Custom code needs to be applied to the page where the chart is. Depending on what you're using (Gutenberg blocks, or some page builder), adding the CSS or JS can be done in a few different ways. 

If you need help with adding custom JS to the page, please take a look at this article.