Store not wanting to take goods within 7 days

This is on behalf of my mother who had to deal with Exact Store at Oxford Street in East London. She bought a Samsung Z4 on ? October and returned it within 7 days because the phone didn't have network. When she got to the store, she was told the phone will need to be sent to Vodacom for repairs and she said she wanted to cancel the contract seeing that the phone needs to be repaired from week 1. The store sent the phone to Vodacom anyway.

I called the store on the 15th of November and spoke to Susan who confirmed the above and further told me that Vodacom couldn't fault the phone. However, she said she can't authorise a credit note only when the phone is back she will speak to her area manager about the credit note. Yesterday a certain Yanga called my mother instructing her to go fetch the phone because Vodacom didn't find any fault. My mother maintained that she returned the phone and that's that. This morning, I called Susan to find out what happened, she wants my mother to go the store to write some letter she can send to their head-office. My mother is not going back to the store, she returned the phone within 7 days because it was not working and she made her intentions clear on day one. Exact needs to deal with this.