How did my bill go from R 599 to R 4367?

<p>I received an upgrade of an iphone6s Smart S package with 200mb ,75 mins and smses for R599 but no this amount has been growing every month .I was given 10GB for the first for the first two months and have called the customer service centre to ask about this i was told it was a once gift from vodacom for the upgrade but now I am having a bill of R4 367.68 .when the agent called me foar an upgrade they never told me that it is an open line contract and in July 2016 i asked them to change it but my request was never attended and when i called them they said i was to pay R599 for the phone as per our agreement at the time of the upgrade ,i have been requesting for this contract to be changed but no it has not been ,i have been given this reference numbers 1- ********** 6741 and 1- ********** 6237 .i requested in July for this line to be locked until it has been changed to top up but till date it has not been and vodacom is billing everyday .</p>