I suggest forgetting about speeds for the moment. The speed your are seeing is consistent with an IP Profile of 135kbps, so in that sense the value is "correct". Posting your router stats - sync speeds, attenuations and noise margins would be more useful information.
The problem/issue is to establish why your IP Profile remains at its lowly value; to get this value your router must have synced with the exchange at a line rate between 160 and 256kbps. Such low sync speeds are caused by high levels of noise on the line (between the DSLAM at the exchange and your router), a router fault, or line/exchange equipment fault. The diagnostic work carried out has determined the problem is (most likely) external to your premises, but unfortunately the problem is intermittent and obviously not fixed (permanently at least) by either of the two BT service visits.
Due to the intermittent nature of the fault it is difficult to determine when the problem occurs (probably in the small hours). Plusnet's records should have this but gathering your own information would be useful. I don't think
Routerstats works with your Belkin router, but it does with the Thomson. I suggest connecting the Thomson and recording (plots) of downstream sync speed and noise margin continuously to give you the 24-hour history of these values.
Your sync speed at the moment is 2240kbps which would give an IP Profile of 1750kbps if sustained. Poor for your attenuation but that is probably because the fault has caused your target noise margin to increase to 15dB (its maximum value on ADSL). The problem is that will not be sustained because of the intermittent fault. It isn't essential but having the connection history to hand would provide useful background information for service visits.
The 'connection' under consideration here is between you and the exchange, and your router will still show the connection stats whether you are connected through to Plusnet or not. The Thomson router allows you to 'disconnect' from Plusnet, though I don't know whether the Belkin has that option. For fault investigation Plusnet need you connected to them because they are testing from their end, but the BT tests done from your premises only go as far as the exchange, then into the BT systems. The 'port reset' probably was like a router restart, reloaded its firmware and probably dropped your target noise margin back to 6dB but did nothing to fix the fault if it wasn't that.
My opinion for what its worth.
David
