Dark Vertical line - Dell S2240L monitor

Hi

I am facing some issues with my dell S2240L monitor which i purchased last year. A 2-3 pixel thick dark red vertical line is appearing on the left half of the screen making it difficult to read words which it intersects. 

I have tried changing video(VGA) cables, checking for loose connections, updating video drivers, factory reset, changing the graphics card and using HDMI port as well, but the issue still persists. The monitor is still under 3 years onsite warranty. 

Please advise on the issue. I can't find the express service tag as it is a 21.5" monitor purchased separately and not as a part of complete desktop.

Serial Number - CN01MVD1641803261SAT

Date of Purchase - 04-07-2013

Warranty - 3 years onsite warranty

Thanks