I cannot cancel my free trial of Acrobat because the cancellation page keeps crashing

You could also try a different browser or computer to cancel. Deleting cache and cookies may help also. Disabling browser add ons, especially those very useful ad blockers could also solve the issue.

Try again support. Type "agent" to get a human on the chat. If you get charged, you still have a 14 day grace periode to cancel, but in this case you will need to wait for a (automatic) refund.

Adobe customer care can be contacted by beginning a secure chat session at https://helpx.adobe.com/contact.html?rghtup=autoOpen. Pop-up blockers need to be disabled, you need to accept cookies! If the chat window fails to open, or is non-responsive, use a different device and/or browser to start the interaction.

For support via Twitter:
https://twitter.com/AdobeCare

(see also here: https://community.adobe.com/t5/creative-cloud-services/how-to-contact-adobe-support/td-p/11875703 or here
https://community.adobe.com/t5/account-payment-plan/how-to-contact-adobe-support/td-p/11843852)

Important: Adobe does NOT contact you unsolicited by e-mail or direct message. If you get contacted by direct message from a person, claiming to be an Adobe employee, look at that profile and check if they bear the “Adobe Employee” marking under their name. Adobe support does not use Skype to give you support.
If in doubt, ask the forum.