I think you'd have to wait until your next anniversary date unfortunatly.
If the web bolt on was a mistake not on your behalf it would be prudent to phone CS (4445) and speak to them about it. They may well be able to refund the bolt on and instigate the reactivation of the tariff for this month.
Nothing sucks more than that moment during an argument when you realize you’re wrong. So Ive been told