bad service

I have complain about cellphone i bought from Ackerman's store Samsung A2 on 28 December I used it for less than 21 days then the phone give me problem I took back to Ackerman they tell me they take the phone to repair then I must wait for 21days which I did when the phone come back from repair the phone give me same problem which is the phone switch off and not on anymore i took there 20 February now when i go there to tell them to give me a new phone or my money they refused they give bad bad service I ever had they tell to call where they took the phone cause my is not with them so what must I do to get the phone or money back cause i can't use the that i bought with in a month being repair twice in 21 day's