Log into the old account and cancel the subscription.
Click on this link to learn how to cancel a subscription from Apple. --> If you want to cancel a subscription from Apple - Apple Support
If you cannot do that then contact Apple but realize that you will likely need to same log-in information for getting them to do it as you would for doing it yourself. They need to know you aren't somebody trying to play a mean trick on somebody.
Refer to this page for Apple Support features ➔ Contact - Official Apple Support
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.
This page has telephone numbers for contacting Apple for support and service ➔ Contact Apple for support and service - Apple Support
By the way, you should not be creating new accounts unless you absolutely have to.