Many users faces this issue.
They upload the document but unable to see it in document library. No need to worry in this case.
You just missed one step which was to check in the file.
Please follow the below steps to resolve it.
1. Open the document lib.
2. Click on Document library settings.
3. Now click on "Manage File which have no checked in version".
4.You can see your documents there, select the document and click on "Take Ownership of Selection".
5.Come back to your document library and Check-in the document.
Happy SharePointing :)