I need to get into my iTunes account on my PC in order to get past the passcode on my iPhone. Can anyone help?

Today I decided to agree to the update 12.4.3 on my iPhone 6s with no idea that the result would be it would lock me out and refuse to recognise my passcode!

I've now been locked out of my phone for the last 6 hours, trying various downloads to try and resolve the problem. None have.

I then contacted Apple Support and was in an instant chat with someone who said I could get past the passcode if I had iTunes on my PC. I didn't and I kept getting an error when I tried to install it so the advice was to end the call and try restarting my pc.

I now can't get back through to Apple Support online.

I've managed to install an older version of iTunes but would like help from anyone who knows what to do from there to actually get past the passcode problem. I'm really at my wits end :((

thanks!