I signed up for an Acrobat free trial. I forgot to cancel before it converted to a paid subscription.My account won't let me cancel as it asks me to update my payment method.Please cancel my plan and confirm that no further charges will be attempted

You can’t cancel until you provide a valid payment card. 

https://account.adobe.com/plans

See Subscription & Cancellation Terms

https://www.adobe.com/legal/subscription-terms.html

Thanks for posting, ​@Said+Abrorhon+Yusupov.

I apologize for any confusion you encountered managing your subscription and I am sorry you did not find more value in our services.

As suggested by ​@kglad you are unable to cancel because your account is currently past due. The payment method you used to compensate us for our services was not accepted.

Please click on https://helpx.adobe.com/contact.html?rghtup=autoOpen to speak with a member of our team who can help you end your subscription.

For more information on the cancellation and refund process, see https://helpx.adobe.com/account/individual/terms-policies-and-regulations/adobe-subscription-terms.html.

Please update this public discussion thread if you have any additional questions, ​@Said+Abrorhon+Yusupov.