Please remove this Quizlet subscription for me

1.

You must cancel the subscription yourself.

See -> Delete apps on your iPhone, iPad, and iPod touch

Delete apps on your iPhone, iPad, and iPod touch - Apple Support

• If you delete an app, it doesn’t cancel in-app subscriptions that you might have. While deleting an app, you might see a Cancel Subscriptions option. Learn how to cancel your subscriptions.

If you don't want to continue a subscription you need always to cancel that subscription in time, see the following Apple articles:

If you want to cancel a subscription from Apple

If you want to cancel a subscription from Apple - Apple Support

If the subscription that you want to cancel is not listed

If the subscription that you want to cancel is not listed – Apple Support (UK)

2.

the money wasn't debited to me, because I don't have it in my account. However, I now have a debt, because of which I cannot download other applications.

If you want to make purchases or update / download apps, including free apps, you need to have a payment method on file.

If you don't have a credit card or don't want to use a credit card, you can also use your Apple ID balance as payment method, see -> Add money to your Apple ID balance

Add money to your Apple ID balance – Apple Support (UK)

• If you want to change your card, add first the new card, then remove the old one.
• or if you use your Apple ID balance, you need to set your Apple ID balance as your default payment.

If you update your payment method or add funds to your Apple ID balance, It would take about 1 to 3 business days in order to process.

If you're still unable to update your payment method, Contact Apple Support.