Iphone 6 microphone not working when taking over the phone.
I Have an iPhone 6 which I bought Septebmber 2014. Last week my iPhone 6 microphone stoped working. When people would call me on the phone they would say that they could not hear me at all. Also, when recording on snapchat, the sound is gone and cannot hear anything. I took it to the Apple Store and they relaxed it with another iPhone 6. Now it's literally been a week with this replacement and it HAS THE EXACT SAME PROBLEM WITH THE MICROPHONE as the previous iPhone that they replaced. It's becoming very irritating because I don't want this to keep occurring. I have no idea if it's just my luck and coincidentally got another phone that doesn't have a working microphone. I have made an appointment to visit the Apple Store again. Is anyone else having problems with their microphone? Will Apple give me a yet again another replacement? I really don't like how they give refurbished replacements. I would much rather receive a brand new iPhone 6 out of the box, I do not care if they keep the earphones and charger. Also, the speaker seems to be lower than when first received. The previous phone was in good care, was not dropped and had no water damage. This replacement is a week old and has the exact same problem.
Thanks. I hope I did this correctly as this is my first post/question.
iPhone 6, iOS 8.4