Extremely poor service

I logged a call last month for a billing error on my account, i was billed double after changing ownership of a number. i followed all the procedures and was told the problem had been resolved and i would receive a credit note on my account. Now in the next month i have been billed double one again and i still have not received any resolution. Every time i try and phone into the accounts department of vodacom the phone gets put down and i get transferred back to the customer care department that cant resolve the issue