Contract migration fee

Today I had the worst experience ever with vodacom they are over charging me on my contract which I never agreed to and to top it all their agent promised me that I won’t have to pay cancellation of migration fee, when I got my bill this month it was added to my bill. they first told me changing to just airtime won’t Change anything on my contract but it did and they once again **** to get a sale ,I’m so disgusted by vodacom that is ripping me off, I’m not going to pay my monthly fee until everything is sorted!!!!!and I’m definitely not going to pay migration fee for something I didn’t agree apon.