Plusnet have no control over your sync speed, and your sync speed sets the IP Profile. As they appear from your earlier post to have submitted a fault report to BT Wholesale, it seems unlikely they are throttling you
What is odd that the BT Wholesale test reports above 3Mbps. Are you testing wired or wireless to the router?
If you run the test again it would be best wired, and for you to copy and paste the full contents of both the text boxes on the Further Diagnostics page.
The indispensable man or woman passes from the scene, and what happens next is more or less the same thing as was happening before.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - Plusnet
UnLim Fibre (FTTC). Sync 57584/13846kbps @ 600m. - BQM