I need some advice about my consolidated student loans.?

I have a check for my student loans for 25,000.....its from my employer and I want to pay my account in advance for two years then make monthly payments on my own to apply to the principal. When I told this to my lender, they said that my monthly payments would not even be enough to cover the interest that accrues daily. My question is...if I am paying my account two years in advance, shouldn't whatever I pay go directly to the principal balance? I don't know what to do. I owe around 150,000 and the whole point is to get the monthly payments down to a reasonable amount for me. Help!