Call 4445 and ask them to change your anniversary date.
You will lose any remaining allowances but means you can top up to start with new ones.
Also think about switching to a tariff with more data to prevent issues with data next month.
You can call customer services and get them to change your top up date to the present allowing you to renew your bundle there and then. That date then becomes your new renewal date.
The bolt on’s are expensive and I try to avoid them by paying for a slightly more expensive bundle so I don’t have to worry.
I’ve renewed my bundle early in the manner I’ve described so I know it works.
Keep it in mind for the future.