Want to change credit card but iTunes support is blocking me

No, you are not hacked, if you haven't jailbroken your iPhone, it's not possible.

Read again what posted.

Please check also ⤵️

1.

If you see a message that says "Your account has been disabled in the App Store and iTunes", there is a problem with your payment method on your account, to resolve the problem you need help from Apple support,  click -> contact Apple Support for help.

2.

If your Apple ID is locked or disabled -> If your Apple ID is locked or disabled - Apple Support (CA)

-> Get a verification code and sign in with two-factor authentication

Get a verification code and sign in with two-factor authentication - Apple Support

👉 If you have followed all the steps and instructions and if you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK) 

How can I update my credit card.?

See -> If you need to change or update your Apple ID payment method

If you need to change or update your Apple ID payment method - Apple Support

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Update your payment method on your iPhone or iPad

1. Open the Settings app.
2. Tap your name.
3. Tap Payment & Shipping. You might be asked to sign in with your Apple ID.
4. Tap Add Payment Method, enter the new payment method, then tap Done.
5. Tap Edit.
6. Tap the red delete button next to the old payment method, then tap Delete.

If you update your payment method or add funds to your Apple Account 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.

See also -> Payment methods you can use with your Apple ID

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

fyi: Not all credit & debit cards seem to work with App Store / iTunes Store, try a different one, or preferably a credit card. If your card is not accepted as a paymenf method, you need to contact your bank.

If you have a valid payment method on file, instead of buying or order an App Store & iTunes gift card, you can Add money to your Apple Account balance anytime, no gift card needed, see -> Apple Gift Card - Apple (UK)