Disappointed in MTN

I took a MTN cellphone contract on the 18th December 2020. The contract was for my son a Christmas gift. He opened the box of the phone on the 25th December 2020. We discovered that the phone keeps crashing. We went back to the shop on the 26th December 2020 and was told we had until the 25th December to return the phone regardless if the store was closed. The 7 day return policy no includes the public holidays and the store was closed. The ram of the phone is to little meaning it can't make use of games or Facebook nor any apps. I was not advised of this by the consultant.