my big amount of credit was missing after I log in Skype calling web account

Deactivated Skype Credit can be reactivated using this reactivation site:

https://calling.web.skype.com/account/credit_reactivation

Just be sure to sign in to this site with exactly the same account as you have used with Skype. Be aware that you cannot sign in to this site with your business account.

Based on the available information, there are two common reasons why Skype Credit does not appear in the Skype calling web experience or Dial Pad after Skype’s retirement process started:

1. Signed in with the wrong Skype/Microsoft account
   • The Skype Dial Pad and remaining paid features are only available when signed in with the exact account that holds the active paid product (subscription, Skype Number, or Skype Credit).
   • If the calling site shows a message like “You don't have any paid product right now” or a balance of 0, this usually means either:
     • The sign-in is with a different Microsoft/Skype account than the one that originally held the credit, or
     • The credit has been deactivated.
   • To verify the correct account:
     • Compare the Skype Name shown on the Skype profile page with the Skype Name mentioned in any original Skype emails about credit or subscriptions. Use the profile page at https://secure.skype.com/portal/profile (from context) to confirm the account identity.
2. Credit deactivated due to inactivity
   • Skype Credit can be deactivated if it is not used within 180 days. In that case, the calling web page will not show it as an active paid product.
   • Deactivated credit can be reactivated (if still eligible) via the Skype Credit reactivation page: https://secure.skype.com/portal/settings/credit/reactivate (from context).
   • After reactivation, sign in again to the Skype Dial Pad entry points (for users with active paid products):
     • Web: https://calling.web.skype.com/
     • Or via Microsoft Teams Free with the same account, where the Dial Pad is available for users who have an active subscription, active Skype Number, or active Skype Credits.

If, after confirming the correct account and attempting reactivation, the balance still shows as zero, direct support from Skype/Microsoft is required because only the billing/support teams can review the actual balance and account history. Use the Skype/ Microsoft support entry points in the context (for example, “Contact Skype support” or Microsoft billing support) to open a support case and have the billing team check the account and any remaining credit.

Note: Paid Skype features (including new Skype Credit purchases) are no longer offered to new customers, and Skype is being retired, but existing active credit and subscriptions can still be used via the Skype Dial Pad for eligible users.

References:

• How do I make a call in the Skype Dial Pad?
• Contact Skype support
• Troubleshooting Skype subscriptions
• Sign-in problems
• Skype help & learning
• How do I get dialpad in Skype? I want to use my credit - Microsoft Q&A