Hi Boom2bust,
I found your thread while seeking answers for my own situation. Similar amount to yours.
I recently received a letter from Cabot followed up by an aggressive call to my mobile.
Also, a few other threads mention whether Cabot own the debt or are acting on behalf of the bank.
I found it strange that pTSB would pass on a secured debt (even if the house is in negative equity).
The letter I received states:
"...your mortgage account has recently been referred to us for collection by pTSB and we are now responsible for collecting the outstanding amount. Our client has advised .....................ensure payment is made payable to pTSB..."
Key words being referred, responsible and client.
So, at least I can deduce that they do not own the debt. Check yours. I'll post any developments.