Maybe you need to select a new data option. When I had one of those devices on O2, I had a tariff that was 90gb for something like 6 months and I used it before this expiry date.
I went onto the top up page, (you can't add credit to your mobile broadband over the phone) and I had to select a new plan.
Go back onto the top up site and see if you can select a new plan.
If this is happening on a regular basis you might be better on a pay monthly mobile broadband sim only contract.
