I got that message twice already and yes it is definitely a SPAM.
If Fido overcharges, it will automatically (or manually) credited back to your account without requiring any user input from the subscriber (i.e., The Fido Customer Service Representative will initiate the refund process and it will be put back onto the payment method).
The only input required from the subscriber is a phone call to Fido office.
Welcome to the community!
Yes, that is SPAM and not from Fido. As far as I am aware, Fido will not send texts from regular telephone numbers. Messages from Fido would be from one of their short codes. You can forward the message to 7726 (SPAM) for evaluation (see here and here).
Hope this helps