Jipper, the second paragraph describing your dilemma reads disturbingly like new-dog-training problems. I realise that this may in part be due to the fact that English is not your mother tongue. I also realise that it's sometimes difficult for employers such as yourself to understand where au pair help ends and cheap domestic labour begins. By definition, and to repeat what most of the others have said, an au pair lives, albeit temporarily, on a par, or equal footing, with the family.
To avoid future conflict with recalcitrant au pairs, I suggest you acquaint yourself with your responsibilities as 'host' and be prepared to modify your expectations . The alternative is to do the job yourself.