no access to e-book

I am disappointed regarding the handling of access to e-books. I had to change devices and now i cant access a book i purchased, a book I need to study for an exam. So now I have to purchase a new one. There has to be a better way to protect digital content without frustrating the customer. I should have full access to a book I bought otherwise what's the point of buying it? this feels more like a rental agreement instead of ownership. If i had known I would have bought a paperback elsewhere