Mark, I use LibreNMS both personally and professionally:
https://www.librenms.org/
If your edge device offers SNMP access, LibreNMS will most likely be able to auto-discover it's ports. You'll eventually have graphs that you can look at historically to see what your bandwidth usage was vs. what your current bandwidth usage is.
I agree that your ISP should be able to offer some sort of insight to your usage over time, but it's also beneficial to run something like LibreNMS locally in case there is ever an issue with ckt problems or local link problems.
-Sean