Hello shreepa,
This could be due to a variety of reasons, that we don't know given the information in your post. We may need to know more to recommend a solution. With that said, this could be due to not canceling the subscription within the proper timeframe. As mentioned here: If you want to cancel a subscription from Apple
About subscriptions
* If you signed up for a free or discounted trial subscription and you don't want to renew it, cancel it at least 24 hours before the trial ends.
This could also be about Family Sharing, if you are the Organizer. Learn more about identifying this charge here: If you see 'apple.com/bill' on your billing statement
For more specific help, it would be best to contact Apple Support: Get Support They'll have access to account information, so they can assist further there.
Take care.