Changed my internet plan to lower tier, my upload speed went down despite new plan description saying otherwise

I recently switched from Gigabit plus to Gigabit plan as my modem won't fully support the first one anyway (connected via 1G port to my router, so no reason to try and push 1.2G through there). The plan description states 1000/100Mbps speed. While I am able to get close to 1000M download when I use direct ethernet connection to modem, the upload hovers only around 22-23M regardless of the time of day. How can I make sure I am getting the service I am paying for?

Regards,

[Edited: Personal Information]