Bad service

Yesterday I visited a vodacom shop at Alberton for cellphone contract and I signed for 24 months contract. After I have reached home I received a call from vodacom at Alberton telling me that my sim card is not yet activated and they are still trying to activate the period of the contract and I was asked to change the contract period to 36 months as they are having difficulty to activate my contract to 24 months, to my surprised I received 2 smses to advise me that my contract was activated,one sms I received while still at store and another while at home and I even asked why I have received 2 smiles and I was told it is one contract and I won't get charged an additional amount. Boom today I received a call from them again telling me that my contract can't be 24 months but 36 months or I will have to return the phones. I feel like I was ****** as I had enough time yesterday to look for the contract that I will be comfortable and I couldn't since vodacom pretended that they are giving me 24 months contract while knowing they are going to change it later. I won't return the phones and I will take the contract as per what I have signed for.