Unfortunately,you appear to have little understanding of how a loan(mortgage is a secured loan) works.
Interest is charged daily on the cleared balance(not on the payment).
So if you pay twice as much,your balance and therefore your interest bill are reducing much quicker.
(Think about it.if loans worked like you are saying then if you only paid €1 a year then you'd only pay 3c in interest !)
Edit:the second part of your reply is true in that you get most of the interest relief in the early years of a mortgage simply because you owe more.