Hi Nicky
My apologies about the late reply.
I personally do not have much experience in regards to Draytek and USG, however I had a quick look online and I can see several posts on the Ubiquiti forums with customers having similar issues. If you are unable to get a resolve here I would recommend going over there to take a look - There is one post that pops up immediately that references the same equipment in your question - I'm not sure if this will be any help or not but you can find that here.
If you take a browse around there hopefully you can get this sorted, and if you are still having issues - depending on your package with ourselves you may be able to contact our Enhanced IT Support Team on 0800 500 247 (they are usually chargeable, but you get the service free if you have an Enhanced broadband package). If you give them a buzz they should also be able to assist. 🙂
Regards
Ryan