Unsertified with the service

My phone was booked for repairs with vodacom centurion on the 12th December 2015 because the screen was blank , on the 16th December i was told that the cell was ready for collection , on the 18th December 2015 the same problem occur on my cell . I took it to vodacom and was told that they need to send this cell to head office which will take about 21days however they can escalate this . I told them that i have a problem with that because for a period of 3days the same problem occur i need them to give me a new cellphone. The loan phone that they wanted to give me is so pathetic ( ZTE)