How to cancel AWS Skill Builder Individual from AWS Console?

Based on the situation you explained, it's problematic.

I believe, you'd have already followed FAQ -> Individual Subscription

How do I cancel my subscription:

1. Log in to AWS Skill Builder
2. Go to left pane menu
3. Click "My Account"
4. Click "Purchases and Subscriptions"
5. Go to "Subscription Management" section
6. Click "Go to your subscriptions"

When you login to skill builders and get prompted to create AWS account, aren't you able to cancel that prompt and follow the steps outlined above?

Additionally, completely unrelated but still I'd suggest you to give this post a read.

If you are still not able to cancel the subscription, log a case:

Here are the steps to open a support ticket with AWS:

1. Navigate to the AWS Management Console.
2. In the navigation bar on the upper-right, choose Support, and then select Support Center.
3. Select Create case.
4. Choose Account and billing.
5. Provide the details which you shared here and any additional context, which you can give.
6. Click Submit.

Support engineer would be able to help you out and confirm if there is anything required from your side or not.

Here is an article that details the cancellation process. In case you are unable to log into skill builder using your account then I recommend raising a support case under "Account & billing support > Billing > Other billing questions" and AWS support engineer can help with cancellation.