Siri microphone & the earpiece speaker is all part of that top flex cable. Not sure which metal bracket you are referring to but if you're talking about the large one that sits behind the LCD, that missing would have nothing to do with the Siri mic & earpiece speaker not working. Sounds like you need to have that top flex cable replaced. The place you took it to the last time should of offered to replace that for you. I would suggest finding a good reputable service center in your area to take the phone to.
Anyone with over 100 reputation can flag problematic comments and posts.
Oops! I'd like to change my mind.