i have bought minecraft but it says play demo. i have premium over a year

I have minecraft over a year now.Today i wanted to play in a server and so i opened my launcher.When it opened, at the play button it said ''play demo'' and i can't play on multiplayer or anywhere. i can play only demo. i have tried to re-log into the account or even re download it but it says : you have already logged in as a demo user (a big number with some laters) in another profile.you may use this account and skip the anthetication! i don't know what to do.Please help,minecraft is my favourite game.
Thanks for your time