Why instagrams charging me to download it

See -> 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)

👉 You may need to have a payment method on file, even if the app you want to download is free. 

Check which payment method you have on file and make sure it hasn't expired, been declined or failed.

See also the following Apple articles:

Add money to your Apple ID balance

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

Payment methods you can use with your Apple ID

Payment methods you can use with your Apple ID – Apple Support (UK)