Mic not working Iphone 16 with wired headphones and adaptor - have tried most fixes

I have a pair of JBL wired over ear headphones. On my old phone (iphone X) I used a cheap third party adaptor to plug in to make phone calls - no problems. Now I have an iphone 16. Have a new adaptor, that is supposed to be compatible with Mic as well as just Audio, but no-one can hear me, although I can hear them. I've been through every 'fix' I've found on forums, I think, and now not sure that all my settings (sounds and haptics; privacy etc) related to headphones are correct, as I;ve changed them so many times to try and get these things to work. I've done 'forget all USB audio accessories' etc etc, restarted phone, and still can't get it to work. I'm an oldie, so any help would be appreciated. Thanks in advance.