Misled by Vodacom telesales person!

A couple of months ago I upgraded my contract to a contract that included the handset, 600 minutes and 1G of data, cost per month was R1412. Then a couple of weeks ago, a lady from Vodacom Business phoned me. She said I could pay R200 less, and get 200 minutes more if I changed my contract. I immediately agreed, and my contract was changed. Beginning of April I was billed R1903, and my Vodacom app says I will be billed R2535 this month. Today I went to the Vodacom shop in the mall, and they said I could not fix this problem in the shop, I have to phone Vodacom Business! I have been misled, and would like Vodacom to immediately fix this! This is false advertising, and it is costing me time and money!