empty promises by technician

I purchased a cellphone on 23rd may 2015,my invoice number is CA***.Within three months that cellphone was no longer charging and it was swtching off on itsef.On the 4th september I booked for repairs,I was told told to collect after 21 working days.I went to collect as I was told but I was told that my phone is not fixed.I went there every weekend but nothing help.I phoned customer care all I get is empty promise.Today I was told to collect new phone but when I arrive there no stock.They sent me from pillar to post vice versa.I do not know what to do please help