Vodacom promised product change without cancellation.

January I received a call from Vodacom saying they are upgrading existing 5 gig data to 10 gig and changing router to black at same price to retain customers. I agreed and after receiving the new router it was still white & late January my account was debited which raised my suspicion why now am I charged , on enquiry I discovered a new contract added to my profile & Vodacom discovered agent **** to sell me this. The agreed resolving process was that the existing 5 gig data line would be exchanged in May when one of my existing contract expires with Vodacom. This 5 gigs is same price as another handset contract and Vodacom will exchange the contract product for me without effect to cost as I was ******* to get a total of 15 gigs which I can't personal use all in a month. I have called them now in April to request the product switch but they are now refusing me that agreed 5 gig exchange and saying I must pay cancellation fees to switch the product to Handset . This is now shocking me as we had an agreement to just switch product offered to me as customer without any effect on my valid contract profile- only the expired contract will fall off . Can this be sorted out as not I don't believe the telephone sales staff are honest in dealing with customers. I want my promised product change in May 18 as promised without cancellation of any contract. Thanks