Upgrade Lies

My contract finishes in September 2018 i was offered an upgrade at the end of June which i took, when i upgraded i inquired if i will be double charged with new and old contract were the sales person said no. Bear in mind its a top up contract. I now receive abill for both contracts for the end off August, if i knew this i would of waited and canceled my contract. i called customer service which was no service at all, Vodacom is the most pathetic network to deal with. And i regret renewing my contract with them i will never again.