did you lose the private key? if it is lost or has been stolen then it is total and 100% of your bitcoin cannot be returned, unless you save it in exchange and you lose the private key then you can request a private key in exchange
Everything that has a disadvantage also has an advantage. Using an exchange to store your coins, a lot of people will tell you that is a bad idea. But it is more easier to recover your coins if it's stores on an exchange than when it is stored in another kind of wallet. Buh… whatever, the main important thing is that everyone should be very careful when making use of this cryptocurrency.
No one has time for such and by the way there is no way for you recover any coin that is already lost. It's only the owners that. An get to it and that'd if they, themselves, has the key to it. If they don't have access to it then no other Person an have access to it too. If we all can have easy access to coins like that then where's the safety in this then?? That means you will also have easy access to the ones that are not lost too