BILLING MY ACCOUNT FOR CANCELLED CONTRACT

IN JANUARY AN AGENT CALLED ME FROM MOBI TALK , SELLING A PHONE WHICH HE SAID IT HAS A DUAL SIM CARD, ON DELIVERY THE PHONE HAD ONLY ONE SIM . I PHONED THEM AND SAID THEY WILL SEND A COURIER TO FETCH THE PHONE AND THEY WILL CANCEL THE CONTRACT . THEY SEND ME A MESSAGE CONFIRMING THAT THEY HAVE CANCELLED . MONTH END OF JANUARY THEY DEBITED MY ACCOUNT, I PHONED THEM AND THEY SAID I CAN REVERSE THE MONEY WITH THE BANK.MONTH END FEBRUARY THEY DEBITED AGAIN,THEY ARE STILL DEBITING MY ACCOUNT EVEN NOW EVEN IF I DON'T HAVE THE PHONE