Well I have tried the 211801 firmware and that's not made any difference.

Have also replied to the Draytek Support line and provided screen shots of my QoS detecting the VoIP traffic correctly etc.

One thing Draytek Support did ask me to do was to run a broadband speed check online. I did this and these were the results over 4 tests:
Download Speed: 1226 kbps (153.3 KB/sec ) Upload Speed: 646 kbps (80.8 KB/sec )
Download Speed: 1180 kbps (147.5 KB/sec ) Upload Speed: 650 kbps (81.3 KB/sec )
Download Speed: 948 kbps (118.5 KB/sec ) Upload Speed: 556 kbps (69.5 KB/sec )
Download Speed: 1596 kbps (199.5 KB/sec ) Upload Speed: 654 kbps (81.8 KB/sec )

Interestingly on my QoS Setup screen it shows the WAN1 bandwidth as 1359.12Kbps/809.83Kbps.

Obviously it has detected this figure automatically when the WAN connection is established. I wonder if.... because this figure is HIGHER than my actually bandwidth being received by the speed tests that this could be causing my issue? I would happily set the QoS WAN1 bandwidth to approx 1000Kbps/570Kbps if it would then get the VoIP the right amount of traffic, but there isn't an option to change this figure for the WAN1 connection, only for the WAN2 (Ethernet) which Im not using.

Anyone know how I could change this figure to give it a try??

Sorry to drag up an old thread, but did you have any luck configuring QoS correctly in the end?
I have a Vodafone Suresignal box connected to my Vigor 2830n but also cannot seem to get the QoS rules right/working as intended.

Same thing as you - I know that if I'm maxing out my connection downloading from usenet/Steam/Youtube/uploading to Amazon Clouddrive etc, then the Suresignal (and therefore the call quality) will be almost unusable.

I'm on BT Unlimited ADSL package connected at 7616.00Kbps/448.00Kbps.

Any suggestions?