Using itunes store balance to pay for Icloud storage upgrade

Hi, I've run out of storage on icloud and urgently need to upgrade. Unfortunately the debit card linked to my account has expired and it will take me a couple of weeks to get a replacement as I'm out of the country. Because it has expired, I get an error message when trying to enter its details into "Payment Methods"

I have $25 on itunes store balance (added via an itunes store gift card) and thought I can use this to pay for a few months of expanded storage. But on my phone, the only 3 payment options I can see for icloud storage are Credit/debit card, Paypal and Apple Pay. None of these are options currently.

How do I get Apple to use the $25 itunes store balance I have? Added it just now so that I could use it for storage- feel like an idiot for having done so if it can't be used to pay for icloud storage.

Thanks