So my little sister subscribe a spotify premium and my mom have to pay the bill. But, she rarely use the premium feature and eventually delete spotify. My mom want to unsubscribe the premium plan but my sister forgot the password. Even the email password. She is 12. So how to stop the subscription? The bill was added to my mom phone bill. If my mom cancel her now phone number service and change to other phone service, does the premium subscription that come with previous phone service will cancel too?
If the bill was added to your mom's phone bill, this should mean that she subscribed through the phone company. In such case she needs to contact the phone company and ask them to cancel the subscription. Should be possible without the need to change the company but it depends on the contracts she has.
Hope this helps. If you have more questions, please let me know.