on 30-07-2021 08:21
on 30-07-2021 08:28
The simplest way is to change your tariff to the £20 / 30gb one https://www.o2.co.uk/shop/sim-cards/pay-as-you-go
You can change back after 30 days.
Changes can be made in your MyO2 but if you need it before your normal anniversay date, you'll need to call 4445 to start it early.