Debit orders persist after account closure. Basically theft.

I had an account (credit) that was closed and paid in full. Written confirmation of closure received. For months they have continued to deduct an amount without authorisation from my current account. They do not respond to emails nor calls. I have tried to stop and/or reverse the debit orders but it repeats monthly despite all efforts. Worst service ever and be warned....they will leach off you relentlessly even after severing all ties. Is that how they gain a passive income. I'm fed up with Discovery Bank. Please run away from them at all costs.