Vertical fluorescent bulb won’t budge

This single fixture hangs over a stairwell at work and has been operating for a decade, possibly longer. It’s gone out and I cannot for the life of me remove it to replace. I can reach the lowest point of it from the stairs but would require a specialist ladder to reach the ceiling.

I’ve tried pushing in and rotating, I’ve tried twisting, I’ve tried pulling straight down.

All ideas and help very welcome!