Vodacom refuses to cancel contracts when it ends

My contract with Vodacom was supposed to end in August and I did call and gave them a notice of cancelation on the 1st of July. Vodacom continues to allocate airtime to my number and charges me monthly, I have been calling them every month since August and the consultants keep on blaming the previous one for not canceling my contract. I am fed up, Vodacom does not want to let go of their customers when contracts end.