Issue with TRUE zte F668 router DMZ

I have been searching for this information, apologies if its here already, but I did not find and ahve been working at this for more than 24 hours.

For purpose of security for work I am trying to set up vpn router.  I have the router asus rt-68u and I am trying to put it the DMZ of ZTE F668.

I saw stuff from crossy amongst others on web that in DMZ of isp will do the trick.

so I set it up, However, I can connect to my new asus by wifi 2.5 and 5Ghz and login to play around with router.  However have not yet managed to get it to broadcast wifi.?

so I have it in dmz, can get access to it, but that is it.

Have no idea what to do with it now.

I basically followed crossy off the top of head method.  This is driving me nuts as I though it would take me 1 hour tops.

I now have a hole in the wall which True helpfully drilled then decided to leave a trip hazard at bottom of stairs. luckily I came home to prevent the comedy getting any better - ( did I mention how the kitchen fitters dealt with the issue of a slop in purpose built cupboard by taking hammer to brand new appliance?)

So do I need special info from TRUE? should I switch isp?

my feeling is the zte is totally naff, I'm no expert but its wifi broadcast is not ac so I assume its old.

Please help oh and let me know if I'm missing any info.