Recall this from the early days of the ADSL roll-outs but don't recall this happening on FTTC ever
If you have open reach modem plus a router, have you tried turning both off for a few seconds and back on.
Sorry, it's a bit unclear what you meant here, and I'm sorry but that is poor advice as well.
Stuck sessions have not been uncommon on Plusnet including FTTC especially when the was a lot of network issues last Summer/Autumn, and they still do happen if the PPP is lost due to some ungraceful event anywhere between the user and Plusnet.
In some cases on FTTC, logging into the Router and clicking Disconnect for the PPP Internet session and then switching it off for a minimum of 10 minutes will sometimes clear the stale session.
Clicking Disconnect and powering off the Router should be done before even contemplating turning off the Modem - a reboot will do nothing to help clear any stale/stuck sessions.
If anyone is going to turn off their Modem, it should be turned off for at the very least 30 minutes and preferably a hour to ensure the sync loss doesn't get counted as a drop in connection and it resets some of the DLM counters. But it any event I'm not certain that turning off the modem will help resolve a stuck stale session.
Certainly on 20CN, turning off the Modem/Router for an hour always cleared stale sessions, and Plusnet gave similar advice for 21CN when they had quite a few stale session problems with those Network issues.
Unfortunately, in a lot of cases, it's still necessary to get Plusnet to kill the stale session.
Plusnet customer since June 2003.