Why does it keep charging me $7.37 every time I try to download Instagram?

See the following Apple articles:

If you can’t download or update apps on your iPhone or iPad

If you can’t download or update apps on your iPhone or iPad – Apple Support (UK)

If a message says 'billing problem with previous purchase' or 'verification required'

If a message says 'billing problem with previous purchase' or 'verification required' - Apple Support

• If these messages appear, you might be unable to make purchases, download free apps, or use subscriptions. To fix the issue, change your payment method. If you can't change your payment method, you can redeem a gift card and use the balance to pay for any unpaid orders.