Sorry to say that the domain registration cannot be cancelled which is a standard policy I believe. You may refer to the following agreement:
3.1 Fees. You shall pay Cloudflare the applicable fees for the Registrar Services (“Registrar Fees”) prior to the registration or renewal of a domain. All payment obligations are non-cancellable and non-revocable, and all amounts paid are non-refundable. You agree to pay any and all prices and fees due for Registrar Services purchased or obtained from Cloudflare at the time you order the Registrar Services, unless set forth otherwise in your Enterprise Subscription Agreement Order Form or Insertion Order. You acknowledge and agree that you may be charged Value Added Tax, Goods and Services Tax, or other localized fees and/or taxes, based on your bank and/or billing address.