Sounds to me like someone at the dealership is a bit out of kilter!!
Assuming you have HDD system, you should have, as its a 2010 model.
You get updated via a usb drive. That can only be done at the dealership...find another!! The port is behind the dash cover.
Takes about an hour, and last time I did it .... it was £160. Doubt very much the data would be updated every 6 months...that's bonkers. Map data does not change that much so go for it every 4-5 years or so.
If it's got a DVD drive then you can do that yourself with a newer DVD from the likes of Ebay.