Did you actually try what Xynerise suggested?



This command will check whether this address has been generated by your wallet.


Electrum does give you a new receiving address each time. This is done to increase your privacy.
The above command will clear out whether the private needed to spend funds sent to this address have been generated by your wallet.

To open the console goto 'View' -> 'Show Console' -> then go to the 'Console'-tab.

If it returns true your wallet does hold the private key. In this case it is a network-/sync- issue.
If it returns false your wallet does NOT hold the private key. In this case you somehow copy/pasted the wrong address (maybe clipping board malware ? ).