Well, there are different types of dealers - some are VARs, full service trained/accredited, others are cheaper box shifters and then some just sell on ebay... But DrayTek do care about this - you should ask for it to be escalated if it hasn't already been.

Just as an update we have got rid of the 3900 as it was costing the company too much in down time. Full list of daily problems below.

VPN users would get disconnected several times through the day.
VPN users would not be able to RDP onto servers inside the network and would get an error “An Internal Error Occurred”, the only way to resolve this was to reboot the firewall.
The firewall would reboot itself, Co-Processor would jump between 0% and 98% every few seconds for about 5 minutes then the firewall would reboot itself.
The firewall would lock up and need a manual reboot, the CPU would ramp up to 100% then pings inside and outside the network would hit the thousands of milliseconds and then the firewall would then just stop responding.
Skype calls disconnect constantly.
VOIP calls disconnect constantly.

We swapped it out with an Untangle.com firewall installed onto a spare server we had laying about and works absolutely perfectly right out the box. Not one problem. And bar the hardware is completely free!