Did you change your plan from Quebec coverage to Canada & US?
When you make changes to your plan, they will take effect only at the next billing cycle.
If your mobile internet is cutting often, you may need to contact Fizz support
as per instructions here: https://fizz.ca/en/contact-us
Logon to your account andopen this page during business hours: https://fizz.ca/en/solutions/mobileand wait for the chat bubble (at bottom right).
If you have an android phone, you can also try this fix for the mobile data. It worked for me.
You need to manually edit both APN. For both APN, change "APN protocol" and "APN roaming protocol" to "IPv4/IPv6" instead of "IPv4".