Vodacom contact(less) service for past clients

After cancelling my contract after 18 years with vodacom, they continued to bill my account, and now that my number is no longer linked to vodacom there is no way that i can get in touch with vodacom call centre agent to ask why they have billed my account again. no post service to past clients, makes me wonder if i should ever consider returning my business to them in the future.