It's a NOW supplied VDSL router from a few years ago, but recently I wanted to setup some reserved IP addresses and custom DNS, I called up NOW and got the router password and set it up and everything worked fine. But each time I restart the modem/router (even using the built-in restart in the routers web GUI) it loses all my settings, including the login password NOW had set.

So each time there is a power cut, or I restart it I have to call up NOW to get the password changed again and re-setup the DNS and reserved IPs.

Any ideas why it's not holding my changes? (NOW doesn't know, and wants to sell us a new VDSL modem/router, I'll probably source my own)

PS, I've tried holding the reset button on the router and it'll reset, but doesn't fix the issue.