Why would you expect your mortgage payments to go down? What sort of a rate are you on?
You may be confusing the fact that at the start of the mortgage, more of your repayment goes towards paying interes as you pay more interest at the beginning as the balance is higher. But as the balance starts to reduce, your interest is lower & more of your repayment goes on clearing the balance.
Bu tthis has no bearing on your monthly repayment.