Sorry to hear about your difficulties. Generally with such a codeshare the interaction with the issuing carrier (here EK) ends with ticketing. Check-in, seat selection, lounge etc are generally all provided and managed by the operating carrier (QF). While there certainly seems to be some misunderstanding as well as poor service and handling from both airlines it sounds like mostly this is an issue you have with QF, who were unable to allow you to assign a seat, check-in online and failed to inform you which lounge to use (LHR has a specific rule that you just use the operating carrier's lounge). Thus perhaps this thread belongs in the QF forum.

Do you know why you were booked in the codeshare and not an EK-operated flight or a QF-issued ticket? Perhaps you can ask your travel agent to not ticket you on codeshares in future. Have you written to QF to complain about specific issues (leave the emotion out of it).