Incorrect Upgrade

My Vodacom contract expired June/July last year. I have decided to cancel the contract in February and contacted Vodacom's Upgrade / Cancellation Department. The lady convinced me to at least remain on a data contract. So we agreed on a 3GB x 24 months contract upgrade. She indicated I have 7 days should I wish to change the contract upgrade. I called Vodacom within 7 days and changed it to a 2GB x 12 months contract. 1 March the upgrade came into affect, and it was a 3GB x 24 months upgrade. Since then I have called Vodacom numerous times and to various departments to correct his and each time I am sent to yet another incorrect number. My frustration is that I have to call them to sort out their mistake. Each time I am holding the line for 5 to 10 min to be told it is the wrong Department.