Dunno if you have any form of contract with the Grauniad? If so, simply cancelling the DD might (read probably will) put you in breach. If they’re arsey they could put a ding on your credit file…
Go here: https://www.ccw.org.uk/advice-and-support/households/
If still no satisfaction, go here: https://www.ofwat.gov.uk/regulated-companies/investigations/how-we-investigate/complaints-disputes-can-help-with/ and make a WIA91 claim.