It does not exists a plan with 3Gb
Therefore, you used 10gb, did you check the utilisation in your phone?
Rember data have an expiration too
10Gb are alot, but I do not know your utilisation, probably you will be better off to contact the support
To contact the support you need to go to this page https://fizz.ca/en/contact-us, Fizz push you to find your solution, therefore, you need to search in the solution hub to your solution and only after 10 seconds that you are in a solution page Fizz will give you the chat bubble.
If the chat bubble does not appear, this means that the number of sessions waiting for our answers surpasses our processing capacity. If that happens, send us a private message via Facebook Messenger or Twitter.
Your can also send a message via facebook messanger https://facebook.com/fizzca and click send a message (this is a bit slower)
You can also fill a contact form from your account Once logged in, from the account panel go to My Profile → Contact Form (the subject are limited) and fill out the form and someone will email you back.
When is your billing cycle? Is is possible you have 10 GB that expired (plan data, gifted data, perks data that carried-over from previous cycles).
If you go to your Fizz account web page, Data Utilisation, you will see the expiry dates for all the data carried-over and received during the month. You can also check-out for the previous cycles.
If this does not explain it, you should contact Fizz Support in case it was a bug or something on their end.