I was reading only yesterday of two gang members jailed for 4 years each for stealing at least 26 cars they could be linked to. They were both from Lithuania but no doubt there are plenty more like them out there of all nationalities. I guess that four years means they'll be out in less than two for the theft of £1m of other people's property.
The cars were taken to a unit in Peterborough where they were literally chopped up for export as parts. It was also reported that a number of jamming devices were found to stop the vehicle emitting location signals which may explain why the Mercedes Me app didn't help the OP.
We regularly discuss this topic on here but it seems there is still a widespread lack of awareness of theft linked to keyless go . I agree with
@AMGeed, why do the dealers not inform the customers? Also, it shouldn't be too difficult for DVLA to include a theft reminder with (or even on) the vehicle's registration document.