Note that most of the links in the post by SravanKrA (many of which have no relevance to the situation as you describe it, so you do not need to read most of them) will take you to the Apple India version of Apple's documents. Typically there is no difference but there could be and I suggest you follow links I provide which will render the version appropriate to your location.
If you cancel a subscription you may have to do it at least 24 hours in advance of it renewing or you will still be charged. Have a look at: If you want to cancel a subscription from Apple - Apple Support
If there's an issue when updating a card, add a new card first, then remove the old card. If you need to change or update your Apple Account payment method - Apple Support
If you still have problems adding a card, contact Apple. 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 under “Get more help” (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 support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple Support - Apple Support For some countries look under “Other” listing at the end of the list. Not every country has telephone support, and phone numbers may only work when calling from the same country.
