Four months of waiting for a cell phone repair

My nephews father bought. Him a cellphone which was under gaurentee and insured , during this period the cellphone stopped charging and went off and didn't come back on , My sister took the cellphone back to the store to have it repaired, the store told her the waiting period was four to six weeks , she went to pick it up when she got home and open the package the cellphone had no back cover and no battery so , she returned it this was the week after valentines day in February 2015 , upto date she still hasn't been able to get the cellphone back all they keep doing is passing the buck. She asked me to write to hellopeter on her behalf to try and get some kind of reason why Jets has been unaccountable after so many calls to the store.