Interesting points on the NPS.
Are they still using APS? I was with Westnet when iiNet took over. We were running NPS (Net Promoter Score) and I had recently introduced APS (Agent Promoter Score). NPS is a business-wide score and should not be used to grade employees. That's why we introduced APS. It was for the caller to rate the interactions that they had with that staff member and had nothing to do with their overall feelings towards the business. Essentially if APS was the same or higher than NPS, then the employee handled the call well. If it was less than the NPS then the staff member probably needed to be coached in the area where the call went pear shaped (whether this was discipline/training/etc would depend on the situation).
Having said that, these stats should also not be used on an individual call basis but looked at as an average over a time period. You will get the odd customer or two who just score low for everything because they are upset that their service is broken. If there is an issue with the average (of APS) then the CSM should start having a listen to those calls which brought it down.
iiNet does have a fast paced lifestyle and it is a high pressure work place but the comments from your manager are way out of line. As Nick said below, I'd be surprised if you didn't get a call from someone higher up to discuss your experience with them.
There are some great workplaces out there but also some that are worse than iiNet. The only advice I can offer is to look for something that you enjoy doing and try to find a job doing that. If you're doing something you enjoy then it's like you're not actually working.
Good luck with it all.