bad service

hi, i took a nokia lumia 720 on contract with cellc in august 2013 ,by december 2012 the phone had been returned to cellc for the third time to be repaired . i was told if the phone continued to be faulty cellc would replace it and i should call ***. the phone continued to be faulty after repairs and i took it back to cellc in june 2015 they told me it would take three weeks its been more than three weeks and every time i go to back to them they cant tell me about the phone and say i should call *** to find out about it when i do call that number i get put on hod then the call just cuts I've tried both numbers a few times and im not getting any help