being charged for double the amount

I received a phone call in December 2015 from Vodacom to upgrade my account to XL package as I was depleting my free minutes and data on my current package. I was told over the phone that i will not be paying much more, i will only be paying an extra R100+- a month. I decided over the phone to upgrade according to the consultants advice and because i was told it won't be much extra, she also told me i will not pay anything extra the next month, but i was double billed in January for the previous package and the current XL package. <br> <br> I called support a couple of times to get an answer as to what is happening, i got hold of a lady who said they will investigate the upgrade phone call made to me and come back to be with a response. I have not heard anything back. I need to get to the bottom of this as i was misdirected over the phone, if i had been told about the contract being double in price i would never had migrated. I would also like a copy of the phone call please.