why not accepting default key password ?

The default password is written on sticker label behind the modem. Or it was supplied by the install technician if it is different.

You can see Fizz FAQs concerning internet here

https://fizz.ca/en/solutions/home-internet

As Fizz tells us here https://fizz.ca/en/faq/what-are-wi-fi-technologies-used-fizz

"If you do not remember the password you entered during setup, reset your Wi-Fi modem to its factory settings by pressing the reset button on the back of your modem for ten seconds."