By special regulation of the European Union, as of 15th February 2016 throughout the EU, online purchase disputes will be possible through the ODR platform that is accessible here.
This means that if you encounter a problem during an online purchase within the EU (defective product, inability to substitute products, etc.), you can submit your objection in a quicker and simpler way at the top link.
The platform can be used by consumers and merchants, and the complaint can be submitted to any of the 23 official EU languages.