Take your phone back to the shop to get it looked at, there might be a problem. Iphones are overglorified piles of junk anyway.
It was a stupid idea to get a really expensive phone if you are only using it for job applications and general calls. You pay more than £20 a month for a phone if you use apps, games and the internet a lot. If you're just using it for texting and calls then you should just get a standard smart phone.
I pay £17 a month for my Sony Experia and for that I get unlimited calls and texts and 2GB data. It's a good phone and it has PSN which is good for me because I play my PS4 a lot.
I used to be an Apple fan. I have an ipad, ipod nano, ipod touch, apple TV. I even made my i pod nano into a smartwatch using a kit i got off of the internet. But then they kept releasing stupid updates I didn't want and all they did was make my apple toys into slow piles of quickly outdated crap.
I have now sold my soul to Sony, because their stuff lasts longer and does a better job.