I, the good cop, mailed a long rant to the PTCL Broadband manager, Mr. Ali Raza Baloch, last week, after getting his email from the helpline.
He forwarded my complaint to a couple of relevant people, asking them to help me out, but that didn't happen.
Meanwhile, a friend, the bad cop, sent a written complaint to PTA – the PTA people wrote a letter to PTCL, and PTCL called my friend, and promised they will upgrade 'tomorrow' – which happened to be a local holiday, so 'tomorrow' never came.
Today, my friend went in person to the Broadband office, spent two hours there, met Ali Raza face-to-face and explained the situation to him. Ali Raza contacted his team, found out that my friend's upgrade was stuck in Islamabad somehow, and got the wheels in motion for him. My friend did manage to get my connection upgraded in the process though – so when I woke up today, I found my modem connected at 510kbps.
So, for anyone who is desperate to get the promised upgrade, you can be proactive and follow the same route instead of waiting for something that PTCL owes you but is reluctant to provide. I'm getting about an 80% throughput – 410kbps or so, which is good enough for jerk-free Youtube, and the upload speed of 300kbps is helping me save a lot of time as well. 20$ for 512kbps is still about 6 times more expensive than the 50$ for 6mbps that my American friends enjoy, but I hope we will get there eventually. Thank god for competition.