Cellphone purchase gone wrong

On 12/7/2015 i bought a samsung J1 cellphoneby Foschini Cape gate on my Markhams account. When my son start using the phone was struggling to open the applications. Then I took the phone back 17 July 2015 and it was sent for repairs. After 3 weeks I went back to the store to find out if the phone was repaired. I informed thecashier that im not happy and would like to take a new phone cause it will probably give problems again. She told me I can choose a new phone but didnt credit it on my account and the phone was still in their possesion<br> I received a statement from Markhams end of July and sms for the instalment that is due.On Friday 25 September 2015 i went back to Foschini to ask if i can take clothes in the place of the phone as its been with Foschini and i could not use it.How can i pay for something that i am currently not using. The Store manager refused to credit the phone and said i must take it cause it will lie there until next year<br> Can someone please assist me. i did my part in taking the phone back within the week it was purchased, No one contacted me the time is was in for repairs. How can i be expected to take a phone back that i dont want? Please help