Bad attitude and *****

Yesterday I went to enquire at Vodacom if I could open a contract with them ,Shahida did an application and it was approved there and then, even without all the documents, I only had my ID with me and she said I must go get my bankstatements and the rest Ill submit later on when I get a chance, she explained the deal (contract ) for me for the Samsung G7 for R250 pmonth and said I will get R110 airtime monthly and would be able to recharge thereafter when I run out of airtime, I was happy and thought it was a good deal, then she said I could take the phone if Im interested ,so I signed everything and took the phone, went back later for a sim swap as my sim didn't fit on that phone,they told me there was a problem with my contract but they were working on sorting it out, Today they called me and told me that the contract was declined and I must bring back the phone,or if I want to keep the phone I must pay R480 upfront and the premium will go up to R369 every month,but that's not what I signed for and agreed upon,I want to know whats going to happen if I bring back the phone as iv already used it because I will not accept the new terms and premium that they now offering me.