A few weeks ago I had a similar problem. I had lost all my English speaking voices and my car icons. I calley TomTom and they did a brief troubleshooting, and quickly told me that it was a mazda issue , call the dealer. The mazda nav "specialist" told me that the head unit was probably the problem. I ask them to humor me and put one of the demo cars sd card in my unit, miraculously everything was fixed, and I kept the demo cars sd card. I went home and deleted everything TomTom from my computer. I then reinstalled tomtom home and updated everything. It all is working correctly now.
I also made an additional nav card by formatting a 8gb class 10 card on my computer (fat32). I then started my car without any card in the reader. When the Nav asks for a card, put it in and let the car format it, wait about a minute for it to finish. tomtom home will recognize the card as the NB1, i could now update all the nav info. I have been using the backup for about a week without a single hickup. I figured I would save the Mazda card for when I have another problem.