car tittle

Change of Ownership in Mexico as Foreign

We have just bought a camper van in Mexico. We've got Spanish Nationality and now, we can't make the change of ownership. We have tried everything and we have tried it in several states in Mexico. I wonder how people do change the ownership in other countries. How do you buy a car in another country? What can I do? Do I need to own the van in order to cross borders in LatinAmerica? 


Thanks in advance