Mtn refusing to take back device.

MTN mall@Carnival store near PicknPay in Brakpan. I'm here to cancel a contract upgrade I made last Saturday on the 4th March and today is Wednesday. Yesterday i was here at the store Catherine the lady who assisted me with the upgrade over the weekend told me to call the MTN Call Centre to check if the was no cancelation fee, I did, the call centre told me that I was still within the and 7 days period, so there's no fee, and further told me I could return the device to the store. Today the same Catherine is singing a different tune, saying that they "unfortunately cannot take it back" with no valid reason whatsoever. She further says the call centre usually gives clients the wrong information , which is the case with me she says. When i ask her why she told me to call the Call Centre to begin with. Secondly i feel like it's a delay tactic from them so that the 7 days lapses and they can have something to hold on to. MTN please advise what should be done in the this instance because they are blatantly refusing to take the device back which has no physical damage or otherwise, it's still in the box with everything i got with.