Rain continues to take money from my bank despite that the account is no longer in use

I canceled my account mid March and it was deactivated immediately there. End of the month Rain took R499 from my account. End of April they took another R499 I phoned them and they said the money will be refunded after I returned their router. I returned the router. Again end of May another R499 was taken from my account without my mandate. Since then to this day I have called them several times only to be told that billing will get in touch. They never did. The whole situation is frustrating