OK, time for another approach. Running as su may cause further problems, leave that at the moment. Fine running Putty from desktop.
KPPP did allow you some access, let us see if we can sneak out some details via the modem tab here.
First, when I open KPPP I see a request for ISP login details, I don't touch this and go to Configure, here I see the modem TAB and enter, a blank screen (have no modem)
If you follow this procedure, ie no login details supplied, what do you see in the modem TAB?