iOS (and Android) uses a global roster of wifi hotspots and their locations to guess your location. Essentially, if any iPhone user has driven near your house before with their GPS on, that iPhone will store your wifi router serial number and gps position, and transmit it to Apple to add to their global roster. So whenever you use maps or another location app, it guesses your location.
However, once you drive into a suburban highway with no wifi routers nearby, the iPad won't be able to guess a position any longer.
Tomtom will only accept true GPS satellite locations, because they are more precise, and they work while on highways. Since you iPad doesn't have a GPS receiver it reports no location found.
Again, call TT support and see what they can do regarding a refund.