Sony M5- Faulty Handset

I received my new Upgrade in November 2015, had it for about 10 days and the phone just switched off. Took it the Cape Rd branch who advised that i had just missed the 7 day return policy, they advised me to take it to their Worraker street branch where the phone was booked in, i received it back a few days later and was told it was a software problem, phone worked for about +- 2 weeks only and then just switched off again. This time i received a new handset from the store. Used the new handset for about +- 2 weeks and the same thing happened again. I booked it in and received it back on 30.12.2015, on 04.01.2016 the Sony M5 just switched off again, my husband booked it in the next day and mentioned that they need to check as they suspect the memory card to be faulty and it has now been sent to a high level of escalating and may come back next wednesday or thursday. How can it be the memory card as the first faulty unit had no memory card.<br> i am very unhappy and dissapointed as no loan unit is given and i am without a phone. I do not want the M5 unit any more and would like to change my upgrade, this phone has been in more for repairs than be of any use to me.