I was charged 29.95 for a subscription that I cancelled

I am so sorry that you're experiencing this.

Please review your bank statement for the charge. If it says apple.com/bill then it was billed through Apple. If you see the actual name of the developer, you will need to contact them directly and get that cancelled.

If you did not cancel the subscription within 24 hours of the renewal date you will be charged.

Cancel a subscription with Apple > https://support.apple.com/en-us/HT202039

You can always process a refund request for the charge > https://support.apple.com/en-us/HT204084

Also you may have another Apple ID or someone in your house is subscribed to the same subscription or a similar priced subscription.

Please review everyones purchase history in the household > https://support.apple.com/en-us/HT204088

If you are family sharing, and the organizer you should be able to sign into reportaproblem.apple.com and view everyones purchase history in your family group.

If you still need assistance you can always contact Apple https://www.apple.com/contact/

hope this helps