That seems a really odd letter. Are you sure that you have understood it correctly?
Let's say that you have ten years left on your mortgage and your repayment is €1,000 per month.
With a normal mortgage, if the ECB rate rises from 0% to 2%, your repayments would rise.
After ten years, you will owe nothing.
What they seem to be saying is that you will continue to pay €1,000 per month, irrespective of what happens ECB rates.
Then after ten years, you will still owe, say, €5,000 - so presumably your term will be extended by 5 months.
I can't see how they can make the adjustment at the end of term.
Their mortgage accounting system will increase the interest charged when ECB rates rise, so you will see your balance.
As Gordon says, they have effectively extended your tracker mortgage. Assuming this is a cheap tracker, then this is great for you.
As it's a variable rate mortgage, you are free to increase your repayments at any time without penalty.
So when ECB rates do rise, contact Pepper and tell them that you want to repay the mortgage by the original deadline and ask them what the repayment should be to achieve this.
Brendan