Cancellation

My contract has ended with Vodacom a long time ago . I did call up and ask for them to cancel it but I am still receiving invoices which is nonsense . How many times must I call to get it cancelled? I did try emailing them recently to get this sorted out but they have this bull**** Tobi which asks for my Vodacom number and a one time pin which I don’t have anymore and regardless of the emails I send , no one bothers to assist me or to even pick up the email I sent and call me . All I ever received was that stupid Tobi support services which is no help to me . I can’t even get contracts anywhere else because it always pick up that I have a contract with Vodacom ! This is bull****