Underline that won't go away

I underlined a paragraph using three _ and then Enter. Now it won't go away no matter what I do. If I delete the space between the paragraphs and combine them, it'll go away but return as soon as I hit Enter. I've even tried deleting blocks of text and retyping all of it, but the line will appear under another paragraph. Is there a way to get rid of it once and for all? Thanks in advance for any help.