You can restart your modem.
Connect your computer directly to the modem via ethernet cable. Run a speedtest.
If all is well, then try the speedtest with your wifi connection.
If you are using 2.4GHz, try disabling it and using 5GHz only. Or vice versa.
check this link for solution https://fizz.ca/en/faq/my-wi-fi-network-slow-how-do-i-make-it-faster
if it is still slow, you can contact Customer Service by chat :
Please check the info provided on the following link: https://fizz.ca/en/contact-us.
You can also send a message by Facebook Messenger: https://facebook.com/fizzca.