X axis line doesn't disappear

I drew a graph without axis lines, the upper one. However, when I added lines by using 'line' command, there black line at the bottom appeared. It looks like X axis line. How can I remove that black line at the bottom?

[dpb]

Post the script and data that built the figure so can reproduce or at least a small sample that reproduces the issue.

[KSSV]

Have you used axis off?

[Walter Roberson]

Which MATLAB release are you using?

After you add the line, what shows up for

get(gcf,'renderer')

[Jan]

Sorry for this question: "when I added lines by using 'line' command, there black line at the bottom appeared." Did you draw the line, which appears? Please post the code of this.