How do i obtain my adsl account username and password from my adsl modem? My old adsl modem is a Huawei SmartA?

My new TP-Link modem router asked for a password and username which my ISP wont provide. Is there any where i can get the info from my modem? Our ISP sucks, the only one in our country, insisted that we purchased a new modem from them which cost $120. We are already paying $75/month.