Reverse of upgrade - CPA - 7 day cooling-off perio

My 65 year old dad visited the shop on Sat, 4 Apr.His intention was to bring his iPhone 5S in for repairs as it overheats and the battery drains rapidly.He informed them that he has insurance on his phone.The sales assistant, suggested that he upgrade his phone.He is on a Red Advantage.He is not eligible for an upgrade and she said he can get a premature upgrade.It was not properly explained to him.The only thing that she mentioned was that he will be paying less but in fact he will be paying more.She also told him that he will get a watch with the phone. He was however not told that he will pay an extra monthly fee for the watch and was thus under the impression that it was a promotional gift.My dad was placed under misinterpretation and he would like to reversed this transaction.Both the phone and watch is unused.We visited the shop the next day to return the phone and the watch but was turned away and told that you can not assist us on a Sun.We returned the iPhone 6, Cookoo watch, cover and USB car charger to the shop on Mon,16 Apr and they accepted it.Today we were informed by them that they declined our request to reverse the upgrade.My dad has been a loyal customer since 1994