Answered question
Call foreword doesn't work, it will disappear when it rings on the phone.
It is a known problem. Their call forwarding have issues. When I messaged them, they said they would issue a ticket and try to fix it. It's been a few weeks but still no fix.
Other answers
Consider messaging Fizz on the chat bubble or via FB messenger just to add yourself to the ticket queue for known bugs... maybe they'll work faster...
Forwarding has a bug. Fizz knows.