Poor customer service and wrongfull information

In Nov 2015 I went to upgrade on my current cell phone. The consultant told me I will be billed a extra amount from my normal billing in Dec as i upgraded before the time. I agreed to the extra R100. But the consultant failed to tell me that in Jan 2016 i will be billed again the extra amount for the other head set that i stil have. I had not made provision for this amount, i called the vodacom customer care and was told this. I am very upset with the poor lack of customer service for not letting me no that i will be billed extra for 2 months.