1-
During the firmware upgrade did you master reset the modem to avoid mismatching with previous firmware?
2-
are you testing wired or wireless the speed tests? ... if is wired go to the next steps .. if you testing via wifi connect a cable and try again ... if the speeds are close to the synchronised speeds the network & line is fine
3-
Change filters at socket
4-
Change cable from the lan of the 7800 to the pc
5-
Maybe the time your perform speedtests the network is congested ... try other times such morning afternoon evening night times and see if is any difference
6-
test with the modem only plugged in direct to the test socket
7-
can try master reset all the unit and set back from the begin the settings for your isp
8-
Finally or can try from the begin ... try with another modem, your isp's for example & see if is better
When it gives you the results, click on Further Diagnostics at the bottom, enter your phone number in the first box and get it to run the extended test.
When the test is done it will show you the IP profile. If that is lower than around 5 Mbps then the problem is with BT's DLM due to a low sync sometime recently.
As you have Plusnet, another place to look is in the member centre for the current line speed. If that says around 135 kbps (but BT's test says more) then the problem is with Plusnet's systems and a prod through either a fault ticket or Plusnet's community forums should raise that.
I can no longer get an internet connection, even though the router is connecting. I also get the same problems using another router, so have escalated the issue back to Plus.net, who have reported the following;
DCN fault ODC completed on Question ID : 81306802 , BBFC down
So hopefully a fault will be found on the line next week and resolve my problems.