Cellphone repair

I upgraded contract in November 2014 and received a Apple Iphone 5S. It stopped wotking after only 3 weeks. I handed it in on 11 December 2014 on Job no 037775. By 8 January 2015 the phone was returned to the store as i had to disable security online. I did and the phone was dispatced again to repair centre on 8 January 2015 on Job no TEL040209. Imei ***. i visited the shop to enquire progress. Nicholas Wire gave me his email to enquire progress. On 12 February 2015 i received an email from him to inform me phone will be in store before Friday 13 Feb 2015. I went to collect. The phone was not there yet and he cannot track it! ? On 16 Feb i phone the Credit Verting Dept and was informed that to date the phone is still at the repair centre and is awaiting repairs. They cannot tell me progress. Only that i will receive an sms. When? in 2016? I have been paying 4 months for something that i do not have. Should this not be replaced by now? it was brand new! The service at this shop is uphalling. it is the only shop in the area and has long q's. The staff handling this is most uncooperative unhelpfull. Where do i go for help if the shop who sold me the phone refuses to help?