That's very true. If PTCL services work good to begin with, it will work flawlessly. But if it doesn't, complaints (even 1000) will not help in most cases. So its just luck with PTCL.
I even had to change my landline number, to make it work great, though on previous lines it was working ok. Changing number helps with Internet services, always, but its not very easy for everyone to just change landline numbers.