Calling a number with an extension unavailable?

I tried to call a number including an extension from my android phone using the # to insert the extension number.
It shows as dialing on my phone: 613-000-0000 ext. 0000 (zeroes as placeholders for actual number). When I dial I get the fizz mobile message that "Your current plan does not allow us to connect this call. Please sign in to your account to adjust it".
When I look at my account I do not see an option for extensions or anything of the sort. How do I call a number with an extension?
Thanks.