I have the 8500 setup and DV. Works fine plugged into the hub and into an adapter. All I had to change were the number of rings ( set it to max) before the messaging service cut in, so that the base station answered the call if needed.
Very odd indeed. Just to keep me sane could you try:
You may very well find you’ve still got a phone service to your old master socket. It’ll be a different number but there should be dial tone.
Try plugging your relate phone into that and check you’re getting dial tone.
If you do get dial tone then try plugging your 8500 base unit into there and seeing if you get dial tone on your handsets. So it’s like you had before the change to DV.
Let us know how you get on.