Poor service from Vodacom AGAIN and AGIAN and AGAIN

I upgraded in the middle of December 2019 at Vodacom Shop ********** The lady told me that I will pay pro rata for the old contract, which was a SMart L contract and pro rata for the rest of December for the new contract. I recieved a invoice, dated 01/01/2019 for the line rental of January on the new contract (which is correct) AND a pro rata on the old contract for December 2018, which is not correct, because on my invoice, dated 01/12/2018 I already paid for the whole of December. Vodacom must give me a credit for the pro rata that I already paid for December and not invoice me AGAIN for December on the January invoice. So, this is two credit notes. I spoke to Salome from Vodacom on Sunday the 13th of January, but she doesn't understand my complain and where unable to give me a contact email for either Vodacom mall@reds or Vodachom head office. This is really poor service.