This plastic inside is normal. It is called “safety shutter” that prevents accidental insertion of objects other than plugs into the socket holes. It can only be opened by pressing down two pins simultaneously and firmly. The continental EU 2-prong plug has a flexible and converged shape, so it might seem won’t fit at first and you need to push harder and make it work - We understand that it can be annoying, but after the first time, the shutter will perform much smoother.