draytek seems has forgot this model
there is not update since may and the only beta to try was from the polish site which seems for vdsl is not good enough
the only you can do is contact the support not because they will help but for them to understand one more unhappy user so may try do something more soon

You can try the 3.6.1 never had problem with the vdsl light flashing but you may have to do reset (use the rs file) and not load any back up file from other firmware because may bugs affect as well to 3.6.1
ftp://ftp.draytek.com/Vigor2850/Firmware/v3.6.1/