Hey @wkmaksar1 !
Are you currently using a Prepaid or Monthly service?
At the moment you can only change the SIM card through Fido.ca on a monthly account and if you are the account holder.
If you are using a prepaid service; a change of SIM card can also be done by reaching out to us via Facebook, Twitter or by dialing 1 888 482-3436 from your mobile phone.
If you're using a monthly service, can you give it another try from a different browser and let us know if it works?
Keep us updated!