Write to the PTSB outlining your position,you need to fully exhaust all avenues with your lender in this dispute before wasting money on Solicitors.
I know it sounds a waste of time but have you contacted the Financial "Regulator"?,might be worth a call,but take anything they tell you with a pinch of salt(I have been given very poor incorrect advice from them in the past)
If all this fails,PTSB refuses to put you on Tracker then it is a case of the Ombudsman.
As an after thought was this mortgage arranged through a broker?if so contact him to seek clarity or resolution to this issue.
For whats its worth I am not 100% certain that you have a case but you may have,follow the above and see where you end up...