instance terminate and how to reduce remove bills since i used only free trail.

Hi I am a student,I tried to use free tire from aws services 2 years ago but i didn't used it and I didn't know that it will cost.If i knew that i won't even register for free tire.I am unable to pay that bill. plese help me to solve the issue.how can I delete the activated services and how can I remove the costs that I have not even used?