Vodacom sells contracts with false information

A sales person at the Brooklyn Vodacom store sold me a contract on a Galaxy watch, I needed a watch that could do oxygen readings as I am suffering from long Covid. I specifically asked if the watch had this function. I was told it did. I received the watch on the 10th of Sept, realizing it does not have the function I returned it on the 13th. Vodacom refuses to cancel this contract as according to them I should have known it could not do oxygen readings.