Yes, and these are separate things:
Cancel a Direct Debit → through your bank, and let the provider know. This doesn't cancel the service, the contract or anything you already owe.
Cancel a service → contact that provider directly.
Stop helloBill acting for you → email [email protected] to revoke your Letter of Authority, and we'll stop anything that's still pending.
Changed your mind about a new energy or broadband contract → you have 14 days, starting the day after your contract with the new provider is made. Tell your new provider, or email [email protected] and we'll ask them to stop it. See "Can I change my mind after a set-up or switch?" in this collection.
Water, council tax and your TV Licence aren't contracts you choose between, so there's nothing to cancel in the same way: contact that provider to change anything.