Vodacom Still Debiting Cancelled Contract

I cancelled my contract in March of which Vodacom stopped sending me airtime however, they are still debiting me every month while I have no active contract.

I am frustrated because I cannot walk in to an centre for assistance or speak to someone to assist. All their numbers just go to self service which cannot help at all with this query.

Why it is so easy to take a contract but difficult to cancel?