Billing without authorisation after cancelled subscription

For two years I have been trying to get Showmax to stop billing me as I had cancelled the my subscription, and removed my banking details from the account. To this day they have been billing me. I have sent them emails and spoken to a live chat consultant to request a refund with no joy. The only response I got is they cancelled my subscription which was already cancelled to avoid further charges. I have asked for evidence that I still had an active subscription as on my side is showed I did nor were my billing details available to them. But each month they debited my account. So for two years they have taken money without my consent. I have screenshots from the app that show my billing stoped but they continued to debit my account without it reflecting on their side. Please does anyone have advice, they have literally ****** from me and refuse to refund me?