Samsung cannot repair celphones

On 07 February 2015, I gave my Samsung Galaxy S4 to Samsung's Brooklyn store to send my phone in for repairs, according to Samsung my motherboard had a fault that caused the phone to continuously reboot. I still had three months left on my warranty. I received the phone back on 28 February 2015, a week after I got the phone back it randomly starts to hang and then it will reboot with no prior warning.<br> <br> So on 11 April 2015 I took the phone back to Samsung for the same problem which they did not fix. On 13 April I called Samsung telling them that I want my phone back in a week and if the date was not met I want a new phone. On 22 April 2015 I called Samsung to ask them when I could pick up my new phone since they cannot to a time period. On the same day I talked with Samsung's repair center who said that the phone should only take 5 working days to fix. I talked to one of Samsung's Call center supervisors and told him I'll give them till 25 April to repair the phone. With the ultimatum that if the phone is not fixed by then or if it has the same problem before the warranty expires I want a new phone. I got the phone back on the 23rd but today the phone started with the same issue.