Technical help

First topic message reminder :

Not sure of best place to put this so thought General was the best.
I have a year old Samsung Galaxy s4 phone and really only use it for calls or messages - not capable of much else! Over the past few months it has started turning itself off on a very regular basis (about every 30 minutes) and needs rebooting every time. I don't like people being unable to contact me. I've tried to google the problem and all answers are about the battery getting hot or swollen - not in my case but I've got a new one anyway and still the problem persists. Last chance I suppose is a factory reset but will this lose all my phone and e-mail contacts? I bought it from Amazon so no shop here to return it to. Any help from you clever people would be most appreciated

Hazy, in case you do not get this sorted, just came across THS LINK The "sim free" option is unlocked ... Same cheap phone we got in Italy, even cheaper in the UK!