Thanks for the information! You're right, that message is most definitely SPAM. The providers are doing all that they can to prevent SPAM SMS. You can help by forwarding these messages to 7726 (SPAM) (see here). Once audited, it will be used to augment the SPAM filter. Unfortunately, as fast as these messages get blocked by the SPAM filter, the spammers/scammers find new ways to bypass the filter.
A couple of tell-tale signs the the message is SPAM. Firstly, Fido won't send etransfers via email or text message link. If you are indeed overcharged, Fido will simply credit your account.
In addition, if Fido does send legitimate SMS, it will come from one of their short codes, not a phone number. Admittedly, since spoofing is so wide-spread, it's possible the spammers/scammers could eventually learn to spoof those codes as well.
Hope this helps 😀