Have you tried the troubleshooting steps here?

https://www.koodomobile.com/en/help/why-is-my-wi-fi-and-internet-slow

It just stops working at night? From when to when usually? If the link provided doesn’t help with that, you’ll need to schedule a callback for a technical support ticket.

Link does not work.

This phenomenon appears after nearly 6pm every night, the test network speed is very normal during the daytime, but every night, for example now, the speed is only 0.8M, which seriously affects my online video learning, can you solve it if possible. 

I just guess whether because I live in an apartment, when many people use the Internet at the same time, the speed will slow down. It is estimated that the users of our apartment have this problem. Your company need to improve the Internet speed overall to meet the limit state, we can also meet the requirements of our purchase.

Otherwise what we're actually buying is a few tenths of a Mbps.!!!

Hi ​@Cooper Pengshi, we’re sorry to hear about the internet speed issue! Have you tried connecting your device directly via an ethernet cable instead over Wi-Fi, if at all possible?

If the issue persists you can also schedule a call-back through the Koodo Assist to speak to the internet tech support team for other troubleshooting options. 

Are you saying that others in your building also experience this?

Koodo is a 3rd party Internet reseller. If this is occurring with others in the building then there is nothing koodo can do as the Infrastructure does not belong to Koodo.