Resolved Help! Black bars around image external monitor when connected to MBP

[Weón]

Dear all,

I just ordered an ultrawide external monitor (LG 29WK500) to use along with my Macbook Pro (13", Early 2015). However, when connecting the monitor to my MBP, black bars of approx. two cm (left/right) and one cm (top/bottom) appear around the image. The image on the monitor does not completely fill up the entire screen. Does someone know how to solve this issue?

Additional info

• The settings on the LG monitor itself (Aspect Ratio) are already set to 'full wide'.
• Under Display settings in System Preferences of my MBP, the display Resolution of the monitor is set to '2560 x 1080' (the actual and recommended resolution of the monitor according to LG) and the Refresh Rate to '60 Hertz' (the recommended refresh rate according to LG).
• I tried adding a custom resolution (2560 x 1080 again) using SwitchResX4, however this didn't work and resulted in the same black bars around the image.
• What's really strange is that I hooked up my MBP to my father's LG 29WK600 (with has the exact same resolution and pixel pitch as the LG 29WK500) and the entire screen was filled up, no trouble at all.
• Tried different cables, did not work. Doesn't seem to be a cable issue.
• My MBP should be able to push out an image of '2560 x 1080' as 1) the built-in display itself is '2560 x 1600', and 2) no problems were encountered when connecting to the other monitor (LG 29WK600).

Can someone help me, please?

P.S.
Please find attached (under 'SPOILER') two photos of the black bars appearing around the image.

Spoiler: Photos

 

[DeltaMac]

Can you check that your new display is working properly when connected to a different computer?

Do you get correct, full-screen image when you connect your WK500 to your father's computer?
If you get the same, small image --- return your defective LG display.

 

[Weón]

Thank you for your time and answer, DeltaMac. Much appreciated! In the end, I have solved the issue myself. Apparently, I had to overwrite the external monitor's EDID. This turned out to work perfectly. If other people encounter the same problem, I would suggest to watch the following video and follow the instructions (btw, no need for a bluetooth mouse or keyboard. You can simply plug in a usb mouse and use macOS's built-in virtual keyboard):