InDesign file (with graphs from Excel) - loss of quality when exported to PDF

Hi everyone, 

This has been bothering me for a while so trying to find a solution. I produce various reports in InDesign, these include text, tables, photos and often also graphs. I prepare the graphs in Excel, then save it to PDF (via File->Export->Create PDF/XPS) and then place (link) this PDF graph into my InDesign document. However, often the quality of the Axis texts is poor once I export the InDesign file into the final PDF (attaching a screenshot of zoomed Axis values). I have tried to play with the export settings but it does not have much difference. Also, I discovered, that the separate graph that I export from Excel to PDF already shows this rasterized texts, so it seems the issue happens prior to InDesign (as if Excel does not the graph in vectors). If anyone has any useful tips or ideas how to fix this, it would be very appreciated.