Hi There - Am new at forums so hope that this is ok.
Hoping to get some ideas of things to try to resolve our UFB speed issue. We had fibre connected at home here in Dunedin in early December and it was going great (bout high 20's mbps download and around 8mbps upload, we are on a 30/10 plan) until we had our home phone activated by our ISP then our download speed dropped right of to 2 or below mbps but upload remained about the same.
We have tried factory resets, we have had a new modem sent (ISP thought it might be a faulty modem) but the same fault happened, I have spent hours on the phone to our ISP and have them stumped so thought I'd put it out there for anyone else to suggest solutions.
I have also tried all manner of different combinations of attaching the phone to the modem, to the wall outlet, with and without filter (even though filters are not required), cordless and analogue phones. 
I was wondering if the POTS port on the ONT should be active and lit? But can't find any info on that.
Would telephone cable length under the floor where they activated the remaining copper connections be the culprit?

Any ideas would be gratefully accepted. :) Thanks