Contract upgrade ****

On the 1st of December last year i received a call from Vodacom consultants convincing me to upgrade my Vodacom contract. What happened is that she told me that it will only increase my monthly bill by R10( which was a lie) only to find out later that my bill has increased by R280 which is not what we agreed on.

Please help me with this issue. I would like to return back to my normal package because i can't afford to pay