The real concern is not tripping fraud prevention mechanisms (shipping address different from billing, credit card being used for online purchases in a different country, brand new online account created, package being sent to a hotel, etc.). I've noticed Amazon in general is fairly lax about fraud prevention, and you should continue using your account on amazon.de instead of registering a new one. And of course, notify your bank.

The real concern is avoiding tripping fraud prevention mechanisms. Given the amount of hacking that is going on lately, many organizations are on a hair trigger. Warning flags for them are shipping address being different from billing, credit card being used for online purchases in a different country, brand new online account created, package being sent to a hotel, etc. 

I've noticed Amazon in general is fairly lax about fraud prevention, and you should continue using your account on amazon.de instead of registering a new one. You should notify your bank, but often the problem is not with them (since the store and its credit card processor carries the cost of fraud as well). So, your luck will depend on the store you order from. Shopping in a physical store has higher chances of success.