I cant sign in itunes and app store?

You are sign in here .  .  .  with your Apple ID & Password.

Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.

You can’t merge multiple Apple ID accounts.

Check your Apple ID via your email box, see this Apple article: If you forgot your Apple ID

If you forgot your Apple ID email address or phone number - Apple Support                  

OR see -> Having trouble signing in?

https://iforgot.apple.com/password/verify/appleid

See -> If you can't connect or sign in to iCloud

If you can't connect or sign in to iCloud - Apple Support

Check also ⤵️

1.

If you see a message that says "Your account has been disabled in the App Store and iTunes", contact Apple Support for help.

2.

If your payment method is declined in the App Store or iTunes Store

If your payment method is declined in the App Store or iTunes Store - Apple Support

⤵️

Get more help

• If you disputed a charge from the App Store or iTunes Store, contact your financial institution again to authorize that charge and future purchases from the App Store or iTunes Store.
• If you're outside of the United States, you might need to contact your financial institution to allow international purchases.
• In some countries and regions, your payment method might be declined because of changes to local law. Learn about billing and purchases in Europe or what to do if your card is declined in India.
• If you still need help, contact Apple Support.

3.

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

4.

If you can't connect to the App Store, iTunes Store, or other Apple services

If you can't connect to the App Store, iTunes Store, or other Apple services - Apple Support

-> If you tried all of the above steps and you still can’t connect, contact Apple Support.

5.

If you can't make purchases or update apps, including free apps, you need to update your payment method or add a new one. 

6.

If you get a message -> Your purchase could not be completed, you need to update your payment method or add a new one. 

as what apple says, you can check the following steps:

1.

If you see a message that says "Your account has been disabled in the App Store and iTunes", contact Apple Support for help.

2.

If your payment method is declined in the App Store or iTunes Store

If your payment method is declined in the App Store or iTunes Store - Apple Support

⤵️

Get more help

• If you disputed a charge from the App Store or iTunes Store, contact your financial institution again to authorize that charge and future purchases from the App Store or iTunes Store.
• If you're outside of the United States, you might need to contact your financial institution to allow international purchases.
• In some countries and regions, your payment method might be declined because of changes to local law. Learn about billing and purchases in Europe or what to do if your card is declined in India.
• If you still need help, contact Apple Support.

3.

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

4.

If you can't connect to the App Store, iTunes Store, or other Apple services

If you can't connect to the App Store, iTunes Store, or other Apple services - Apple Support

-> If you tried all of the above steps and you still can’t connect, try this, or this, this, etc.

5.

If you can't make purchases or update apps, including free apps, you need to update your payment method or add a new one. 

6.

If you get a message -> Your purchase could not be completed, you need to update your payment method or add a new one.