This isn't really a question of history. The last time they were used was yesterday, in the Ukraine. Nobody has really stopped using them, they tend to show up in every land war. They were also quite prevalent in the Yugoslav wars. Even in peace times they're employed as security services, going by the new brand of Private Military Companies. Understandably they have PR problems, blackwater/xe/academi is notorious for changing its name to avoid fallout for their business.

Mercenaries still being a "thing", I'm removing this question for violating the 20 year rule. But if you want to rephrase the question and submit again so that it is more specifically asking in regards to the use of mercenaries in Europe during the 20th century, I would highly encourage you to!