Samsung A5 Restart or Switch itself off

Bought Samsung A5 on 21/02/2015 and could not use it for a week after I bought it because they struggled to convert the SIM to a nano. It restarted/switched itself off from the moment I used it. Took it to Vodacom and they said, it's out of the 7 day period they have to send it in for repairs. It went in & out of repairs for almost two months. On 10th April, I received it back after they tried to fix it the 3rd time. Phillip, said that it's not right, if it restart or switch itself off again he will give me a new phone. Needless to say, the phone did the same. I took it back on 11th April 2015 but Phillip was not in. I went back on the 15th April 2014 but Philip was not in. The other manager, Angie, phoned him and ask what to do, he said he will phone Samsung the next day to get a refund for the A5 and he will give me a new phone. I phoned them yesterday, left a message but Phillip never came back to me. Today I received a text, they've send the phone for repairs, again!! I accepted the fact that they needed to send the phone in to be fixed. But to send it in for the 4th time with the same problem is unacceptable. And to lie to your customers is even more unacceptable.