Maybe try live chat again, where i find different live chat advisors gives different responses (where you might be lucky where another live chat advisor may be more sympathetic and helpful to your call).
Also , i agree with you on how can they ask for a screen shot when the retention offer obviously disappeared from your screen, otherwise you would have accepted the offer (seems a daft question to ask).
If no luck with live chat for a second time, then what happens if you try the cancel process again, if you have already cancelled the movie pass, maybe try restarting your movie pass subscription again and then cancel it immediately afterwards to see if any retention deal is offered to you again.
One word of caution is that i have never tried cancelling the same pass twice in the same month so i am not sure if it will allow you and you may be stuck with the movies pass for a further month with the extra month payment (so this would be at your own risk).
@pauline1769 I found reactivating and cancelling again straight away brought up my offer again. If you are not at the end of current month might be worth trying.