Mislead by call agent

Was contacted by an elite mobile agent on 25 November 2020 and said that he is phoning me from Vodacom. He then spoke to me about upgrade options and offered me a deal for 24 months. Then followed the steps and he read me the terms and conditions.

When I contacted elite mobile today the agent said that the contract period is 36 months. This is unacceptable as this was not the period I agreed on.