Did not agree on the amount for the Price Plan increase!

A Vodacom direct sales consultant called on the 28th of October and offered to change my price plan for more minutes and data for an extra R20 a month. I agreed to the price change only to be sent an invoice reflecting an extra +R300 a month increase. I called the call centre on the 1st Nov and spoke to Lihle who promised to call me back as her system was offline. She did not. On the 2nd Nov I called back (spoke to Anathi, who was very friendly) and my price plan was reverted back to the original. However, I am told I need to pay the +R300 increase because the minutes/data have already been loaded on the 1st Nov. I DO NOT HAVE THAT MONEY!!! I agreed to the R20 increase because that is all I can afford. Also, why are your consultants *****! Pull the call recording and have a listen for yourself! ***