Technicolor DGA4134 - how to delete guest network?

tl;dr> How do I delete the guest network?

Now the story:

I have finally upgraded from ADSL to FTTC and needing a new modem decided to buy a (stock) Technicolor DGA4134 as I needed one that supported VOIP.

In hindsight it seems to be a regrettable choice as it comes with no manual, and there is nothing online with the Technicolor website saying they provide no end user support! Not something I thought I should have had to check in advance.

Anyway, I set it up on my ADSL networked and it worked. Now having been moved to FTTC I needed to reconfigure it so was looking around the options again and in the Wireless settings I inadvertently clicked the Add button on the Guest network tab. No are you sure boxes, click the wrong bit of the window and it happens.

Not only did this create a guest Wifi network, which I disabled, but also a guest LAN network. Despite disabling that too, I have lost IPv6 as it seems that it is now being assigned to the Guest network and not the normal one. Going into the Local Network settings, if I click show advanced it shows nothing for IPv6 on the normal LAN network, but my prefix is shown on the GUEST network.

There is no way to disable the GUEST network on here, though I have turned off IPv6 state and DHCP Server settings. And in the Wireless settings the guest tab no longer appears, so I cannot see any way to remove or completely disable the guest network.

I even had a look at what could be done through SSH but the commands on there appear to be hobbled read only ones too and ifconfig will only display interfaces. I also found similar with iptables when I wanted to add a rule so it would log denied external connection attempts, something my old Netgear modem did, but it only supports listing rules. I honestly thought this was supposed to be an expert friendly type of modem? I guess everything has to be done through getting and setting variables, but I have no idea what they are and I am not a hacker to be able to find out!

Anyway, apart from having to completely reset to factory conditions, is there any way to remove the guest network?

I think I have a backup of the settings with everything but VOIP and VDSL configured, but it took ages setting up my static leases (for host files) and port forwarding rules because they had to be added one at a time in a very unfriendly interface. That modem backup files are binary these days, so you cannot just copy and paste rules into them to upload in bulk, is clearly churlishness! So a full reset is a last resort.

Thanks if anyone can help.