I received the same offer when I purchased my TomTom in October and was told by the website to update using TomTom HOME, which then told me there were no new maps available.
Since then TomTom released map version 7.210, which I was able to upload for free.
To check your map version, tap the time/signal strength box on the navigation screen. Your map version will be displayed in the lower right hand corner.
If the highway isn't listed on 7.210, you can wait for the next map, which you will most likely have to pay for if its been more then 30 days.
If you don't want to wait, you can go to your local retail store and try the other devices on display to see if one has a more updated map. If one does, you can try to exchange your 720, but you'll most likely be charged a restocking fee.