Vodacom Damaged My Phone

I have an Iphone 6 plus which has a problem with it's mic. I booked it in the first time to Vodacom Centurion after a lengthy time I received it back however it was still faulty. I then booked it in at Brooklyn. After more than a week goes by I get told that nothing was done on the phone as I need to book it in at Centurion again. I then wanted to collect my phone then realised it was damaged. I was then told by the manager Michael that the phone was damaged by me before checking it in which lead in to a 3 week argument and me providing proof of their brooklyn job sheet and the centurion job sheet that the phone was not damaged on checkin. After many phone calls at my expense they finally said that they will replace the phone. I asked for the phone to be replaced with a regular iPhone 6 as there is a design fault on the plus with the mic. I was told they can't and the phone can only be replaced by the same model on which I agreed. I went yesterday to pick up my phone on which I was told it's a referbed iphone so I'm assuming they just replaced my old phones housing. I want a replacement unit as the referb is still going to have problems wit the mic and maybe other problems