Could you change the service_name to SID and try. Next try specifying the IP in the host. Compare it with this sample

ORCL81.WORLD =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = ORACLE816)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = ORACLE81)
(SRVR = SHARED)
)
)

IF this does not work, I would like you to set the ORACLE_SID=Oracle81 in your environment variable and try connecting to the instance and confirm that you were able to connect by this method.

If it doesn't work, I would suggest that you try reloading your listener as

lsnrctl reload


and try again.
Sam