Stupid consultant

So some guy from cell c contacted me on the 11th of this month to offer me an upgrade to the 20gb package. Which will be 10gb day data and 10gb night data for 199 a month . Because of the 5gb data contract that I have I thought it was value for money so I opted for the upgrade. The consultant informed me that the new deal will be effective from March and nothing changes on my existing package. To my surprise my data disappeared and I though maybe I used it up only to find that the stupid fool change my package to 500mb. Who in their right state of mind would change from 2gb to 500mb with an open limit. I made it clear that I don't want to pay any extra amount but he didn't listen. Now I owe cell C because of their *********** consultant who wouldn't take simple instructions. I need this rectified as soon as possible