Incorrect Billing

I upgraded my contract on the 23rd of December 2014 and was told it will kick in from the first of January 2015, so when the R486 was debited on my account of December usage i had no problem, now for January usage on a contract that is not open i'm debited over a 1000 rand and Vodacom call centre explanation is that it consists of calls and data used in December whilst i was on an open contract. How is it possible that December's account can only be debited in February instead of January? i'm really getting frustrated with this.<br> <br> I need someone to contact me urgently or ill have to reverse the debit order and pay only what i know i should be paying which is R488. You can not tell me that the amount debited on the first of January was for November, that's impossible.