Standard internet connection tests such as speedtest.net only test your connection speed and latency. They do not test for issues such as packet loss and jitter, which have the biggest impact on voice quality, but may not otherwise be noticed in day to day web browsing.
There is a tool called Visualware, which runs a thorough connection test by simulating a VoIP call in your web browser.
To run this test, go to http://mcstest.visualware.com/myspeed/myvoiph5_g711_sipalg.html in your web browser:
Then, run the bcs_service.exe installer that has been downloaded:
Follow the steps and install the BCS Service.
Then, return to your web browser, you should now have the option to run the test. Click "Click to start test" and let the test complete:
Once complete, you will get a results page like the below:
Click on the Summary tab, and you will see a traffic light style system for each test. Green means no problem, yellow or red indicates a problem was detected:
Once completed, please provide a screenshot of the summary tab when submitting a ticket to the helpdesk.