When working with your own repositories or with just updated packages, it can happen, that composer still has something in the cache and just don't want to update.

To clear the composer cache just run the following:

$ composer clearcache


Signs that you have an issue with the cache would be if you put in your own repository, it's not found and you find the following error message:

"The requested package vendor/mypackage could not be found in any version, there may be a typo in the package name"

I checked the naming multiple times and also things like the minimum-stability. In the end what solved it was to clean the composer cache.