Expensive phone over 3 yrs

I recently took took a contract and today was end of my 14 day cooling period. I recently realised I was sold a 512g phone ver 36 months which is steeep. I went to the store to ask for a 256 and n 24 months I was told they can’t change it and that is the lowest option they have. I have been in the website and they have 24 months. The phone is still Sealed I feel ****** by Vodacom