Missing cellphone

My Cellphone has a broken screen and the phone was frozen, rendering it unusable, so I handed it in at Ottery Mtn, to a Dale Miles, on 18 April, 2015. I was assured I would have the phone back within 2 weeks. This device is insured via Mtn. To date I have not heard a word from anybody at Mtn, let alone the insurance. I am ignored via Twitter, Facebook keep asking for my details over and over, and yet still do absolutely nothing. I go into the store at Ottery roughly every 2 weeks, to find out whats happening, and Dale goes onto his computer, and says sorry, it's not back yet. Last time I was there on 25/05/2015 and he brought out a log of all phones handed in at that branch. I could see quite clearly that all phones handed in before AND AFTER mine....had ALL been returned...except mine. I am honouring my end of the contract....why aren't they honouring theirs? I am paying for the contract AND the insurance, yet have nothing to show for it. I am beyond disgusted....I don't know what to do, I am going out of my mind to be honest.