Device still not working

I have been a loyal customer for many years with Vodacom, have all my company phones through Vodacom, with my account ranging in R1000's. In October 2015 I received my upgrade, Iphone 6. In late January tthe phone started giving problems - lack of signal, calls made out - the person could not hear me, i could hear them, calls drop. On the 9th of February my phone went in for repairs, I received my phone back on Wednesday the 2nd of March with the assurance all repairs were done. There has been no change in the device. I called yesterday to report that the problem is still there and I was informed that I would need to rebook the phone, no loan smartphone. This is a business phone, I cannot afford to be \offline\" for another 3 weeks. This is highly unprofessional when a client calls or I need to call a client and neither can hear the other. I would like a replacement device."