I have an 11 MKX with an iPhone 4. Both are updated versions. My VC button suddenly stopped working. When you push it, the radio mutes for a second and then comes back on. The prompt command does not chime nor does it say "listening" in the display. The car has been on and off a number of times and it still persists. I had it set to advanced; I was getting good at it. Now I feel like there's 10,000 things I can't do, lol. Any suggestions?