I was in a similar situation. Basically, I started writing letters as I was getting no where over the phone. When I fixed my mortgage initially, it stated that at the end of the fixed term I would revert to the original offer, yet when they wrote to me at the end of the fixed term, there was no offer of returning to the tracker rate. After 3 months of letters going over and back and me highlighting that part of the agreement of my original offer was to track the ECB rate, they gave me back the tracker. My repayments are now €300 less a month. So, be persistent!