Fido

It's already said 'Select Get this offer' and it will gets activiated instantly, i.e. starting to count 30 days 

Once you accepted, it will show in your myService that there's expired date and indicated it's one time fee.  30 days is counted from the date you accepted the offer

You may try to reach customer service to change?  Not sure, try to reach them through Facebook.  I can reach them within an hour. 

Yes, it said when click accepted the offer, it will charge you right away in your next bill.

I think after you accepted, you cannot cancel it.