Unbearably slow internet

[#1]

I am on unlimited extra fibre broadband so expecting speeds of 60-70 mbps.I am having yet again recurring issues with slow internet speed. This seems to occur every 3 months and usually requires a complaint here and an engineer visit. Most of the time this is fixed without the engineer needing to enter my flat so I don't know what is going on and why this is recurring.

I have done the following tests using the Plusnet hub as usual through the master socket, with front plate removed. No noise on phone line. My normal setting is with a Google wifi hub and I am attaching my Google home screenshot out of interest to show the gradual reduction in speeds over the past few weeks.  As you can see earlier this month I was still getting 60MB/s and now it is less than half of that - really difficult to WFH and do any work video calls.

I can't seem to find Help assistant to lodge a fault so doing it here. I would be grateful if someone can fix this issue ASAP please.

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[#2]

Moderators Note

This topic has been moved from Full Fibre to Broadband

[#3]

@voctave Hi, I've run a test and I can see the slow speeds as well on our side. I do need to ask a couple of questions before we can get an engineer out. 
Has anything changed in your property at all? for example, the location of the router. Has any new electrical equipment been added or moved nearer to the router? 
Have you or if not can you do a speed test when your landline is disconnected, please? Do you get the same results? 

[#4]

No- router has stayed in the same place ans no new electrical equipment. These tests were done with the landline unplugged so I would be grateful if an engineer can come asap. Last time there was some issue that got fixed without them entering the flat.