Vodacom contract

Good Day

I have app**** a Vodacom cellphone contract a Huawei P30 Pro it was advertised as R499 for 24 months but when i was doing the follow up the consultant told me that it is R499 for 36months not 24 months that was on the vodacom app or website the consultant asked me to send the screenshot that shows that the deal indeed was R499 for 24months which i did and i will send it again i want to understand as to why Vodacom cant honor the deal that was advertised on their website and vodacom app? I will attach the screenshot

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