Stories from and about people who feel that they have ‘lost’ their native language are everywhere. For example, in the summer of 2014, the BBC asked the readers of its website to send their personal stories, and published a selection from the many responses which they had received.
What is most striking about these accounts is to what extent they evoke surprise, disbelief and often outright hostility and anger. 
Here is a more or less random collection of such accounts and some of the responses from:
If you have other examples that fit these criteria, please let me know.
Language Attrition 