You will need to install iCloud for Windows. Why you might ask... Because of Apple...
https://support.apple.com/en-us/HT204283
Note: Be warned - it is a horrible user experience to try and downgrade your storage to the free plan and remove the credit cart, however it it possible.
Videos
What happens to my storage If I cancel iCloud+?
Can I downgrade or cancel my iCloud+ plan?
Can I get a refund if I cancel my iCloud+ plan?
So, I am in a very unusual situation, let me explain. I redeemed 3 months free of iCloud+, because I wanted to download my photos from the iCloud website. I reset the device I used to make the purchase so I can give it to my brother (I am on a new phone with a different iCloud account). I want to cancel my subscription before I start getting charged but can't because it can't be cancelled in a browser. What I'm asking is whether it is possible to cancel the subscription from somewhere other than the settings app.
No longer have an iPad or MacBook/any Apple device but forgot to cancel my iCloud service. I just got an email saying Apple charged the expired debit card and I'd like to avoid a phone call with customer service, if possible.
I don't know if it's true but my understanding is that I have to use a Windows device to cancel the subscription -- thankfully, I have a Windows-based handheld PC.
Regarding the expired debit card, does Apple get payment details for the new one automatically or something? The email doesn't list the new debit card, only the original.