Samsung S5 mini gives problems

1 October 2014 I've upgraded to a Samsung S5 mini. Very nice phone except that it doesn't work! It constantly loses signal, then I don't receive any phone calls or messages although it is on. Only when I restart it, the last three or four hours's messages comes through. Once I haven't received any messages or phone calls for two days and when I've restarted it all came though at once. I have to restart it three or four times a day nowadays in order to receive all my messages. I took it in to a Samsung store to be sent for a repair