I accidentally signed up for a subscription and it doesn’t let me cancel what can I do?

Your payment information must be accurate, up to date and match exactly what’s on file with your bank, including the current three-digit CVS number on back of the card. Call your bank to check if they are blocking payments to iTunes for some reason, or try a different card. If you still can’t figure out what the issue is, you’ll need to contact iTunes Store Support directly.

To read more about declined cards:

https://support.apple.com/en-us/HT203005

Manage payment info - Change, add or remove your Apple ID payment method information (Apple instructions):

https://support.apple.com/en-us/HT201266

How then do you know you were actually charged? Did you just received an email about it?

If you see apple.com/bill, itunes.com/bill, or an unfamiliar charge on your statement it might be credit card fraud and you will likely have to contact your card bank.

https://support.apple.com/en-us/HT201382

If you received an email, a message, or a calendar notification about an unfamiliar purchase or subscription, it’s likely a phishing scam and nothing was actually charged to your account. Don't ever call, email or click on any links in that message. Just delete it and you should be fine.

If you want to confirm if the purchase was really made, log into your Apple ID/iTunes account directly and check your billing or purchase history. If there is an unauthorized purchase shown there, you can file for a refund from there using the Report a Problem form: 

https://reportaproblem.apple.com/

Recognize and avoid phishing messages, phony support calls, and other scams (Apple article):

https://support.apple.com/en-us/HT204759

If you think your Apple ID has been compromised, stolen, or hacked (Apple article):

https://support.apple.com/en-us/HT204145

To reach Apple ID account security contact and help directly (navigate thru the options to choose the best contact method other than being sent here):

https://support.apple.com/en-us/HT204169

You have to do what the message says. If it’s still not clear what the issue is, contact Apple directly.

Connect to Apple support by phone, chat, email, and more:

https://getsupport.apple.com/?caller=psp&PRKEYS=

If the billing is incorrect, you can fill a Problem Report form and ask for a refund, but you have to confirm the purchase shows up in your purchase history.

Problem Report forms:

https://reportaproblem.apple.com

The screenshot shows that you already successfully unsubscribed. That’s why the $2.99 plan is listed under options to resubscribe.

Exactly what billing issue?

iTunes Billing history with links to Problem Report forms:

https://reportaproblem.apple.com