If you have lost the SIM then you need to get a new one and activate it on your existing number.
Are you still abroad?
You can get a new SIM in a Fido store or you can contact us to order one. The best option would be to pass by a store so that they can also activate it for you - as you no longer have the old SIM you won't be able to activate the new one via fido.ca and it must be done in a store.
I hope that info helps out!