As far as I know, the Draytek 2926 has a WAN limit of around 400Mb, so many not work with the 1GB Tier.?
As for the speed reduction, try a full factory reset on the Hub as below;
Remove any ethernet cables from the Hub and hold the pinhole reset switch for 60 seconds. Do NOT reboot the Hub, just let it do it's thing. Note you will need the passwords from the bottom of the Hub afterwards, so make sure they are legible.
Try checking with Area faults on 0800 561 0061 or if you have a VM landline 150 as small local faults are not listed on the VM status page.
Post the power levels, Pre and PostRS errors and network log from the Hub. Also setup a BQM to monitor your circuit www.thinkbroadband.com/ping
Once done we can comment. Thanks
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click Mark as Helpful Answer or use Kudos to say thanks