Sorry you are struggling to get answers. Have you ever had a lap just to diagnosis endo or has it always been to treat cysts and the surgeon having a general look around as well? I only ask as it may be that the surgeons you have seen are just not experienced enough in endo. It isn't uncommon for women to have several laps where no endo is found and to then see an endo specialist who does find endo. This happened to a women I work with, her first 2 laps found nothing, she transferred to an endo specialist (not a gynae that just advertises that he has an interest in endo along with a list of other gynae issues!) who then did a lap and found endo, only a small amount, but enough to be causing her pain.
If you have only been seen by a general gynae rather than someone that is actually specialised in endo, maybe try to get a new referral. It may be that you would need to see an endo specialist privately, however often they are happy to transfer you to their nhs list after the initial appointment (which would be £200-300) or maybe speak to your GP about being referred for a 2nd opinion but do your research first and have the name of the specialist you want to see and reasons why you want to see that specialist, you may then be able to be referred to them under the nhs choose and book system x