The only way to get results from Navman is (I have a Navman ICN 520 ST), go back to the retailer and make them chase up the problem. it takes a little time but they seem to know who to talk too. As navman does not want to lose a retailer, also they will not answer emails nor is their website helpful.
Have a look at the price of their accessories what a rip of.
You can get them from Hongkong better made and 1/4 of the price including postage.