Have you tried spraying with Vinegar? CLR is also a product that will work.
I use a bunch of used fabric softener sheets dipped in vinegar. Also have used spray canola cooking oil and a green kitchen scrubby. Amazingly it works. Also leaves a light film to prevent build up.
Cut a grapefruit in half, cover with kosher salt and use as a scrubber.
Lysol Power Scum cleaner in the blue trigger spray bottle with a Magic Eraser or a scrub brush.
Wet & forget shower for a slower, no scrub solution. You can use 2x a week to accelerate the cleaning process then once a week to keep it clean.
USE ALLEN"s cleaning vinegar. spray doors let sit for 15 to 20 minutes and then scrub with MR CLEAN ERASER it also great for removing rust . Most super markets carry the vinegar in the cleaning section