Can't disconnect a caller

[#1]

I need your help. I have received a call via a switchboard, for some reason it failed to disconnect. Now the office has closed for the weekend. Plus Net can't help and neither can BT. I have switched off the phone and unplugged from master socket, still no good. Any advise? Simon.

[#2]

It's the calling phone that needs to disconnect the call unfortunately - not sure why BT can't disconnect it though. It'll need to be disconnected by the switchboard operator I suspect. Is the place not manned at all over the weekend?

[#3]

I presume you can't get a dialtone as the call is still connected.
Who do you pay  for the Phone line ? Plusnet or BT ?
Just call the supplier and report it as a fault , i.e. no dial tone. Surely they've then got to sort it out and reset the line...