Yes, well the first agent just got it wrong. A quick look through the stickies at the top of this forum would help that agent and indeed any other traveller in this position - if your initial purchase was for an Avios ticket you can't earn TPs or Eligible Flights. If it helps, you're not the first person to be caught by this, but that's why there is Flyertalk. If in doubt about something like that you best check here, there is usually an expert online who will give you the correct information very quickly.