After re-reading your original post I may have misinterpreted your issue.
What you are saying is that your odometer reads 6,875 and your Garmin reads 13,675+/- giving you a difference of around 6,800 miles? If so, you need to present that to your dealer. The only thing I can think of that would throw that off would be that the Garmin unit was not factory installed and may have been put in from another car - perhaps the entire infotainment system.
How many miles were on your car when you bought it? From your latest post you insinuate that it wasn't brand new but rather a Demo model or something like that.
Last edited by Seanie; 02-20-2013 at 08:58 AM.