unauthorized charges

I found charges on my business 3G account. when I called in they told me it was pop ups that we subscribed to. but because its a business I had to write a letter on a business letter head to get more info. I was rather confused that extra charges could come off my account requested through my internet that is open to staff and clients but my request had to be on a letter head. I sent the letter to query the charges 12/9/2015 and again 22/9/2015 Ref# EC-0XKK-20KCVT . this month I again have extra charges and to date I only have confirmation of them receiving the complaint. i have been a loyal client of Vodacom and have spent a large amount of money over the past 9 years and this is the thank you I get.