A Microsoft file hosting and synchronization service.
Sorry to hear about this. Since the additional storage is not appearing under your purchased subscriptions and you also do not see the charge on your card, could you please confirm where you purchased the storage—from Microsoft directly, the OneDrive app, Apple App Store, Google Play, or another provider? Also, did you receive any confirmation email or receipt for the transaction from the site, not your payment provider?
Please also confirm whether you are signed in with the same Microsoft account that you used when making the purchase. If possible, share a screenshot of what appears under https://account.microsoft.com/services and https://account.microsoft.com/billing/orders, making sure to hide any personal or payment information.