I have tried everything and FYI, I rent this place and other than that, it’s a beautiful older home.
This is how I clean my porcelain sink...works wonders. Cerama Bryte. https://www.exquisitelyunremarkable.com/2018/06/best-way-to-clean-a-white-porcelain-sink.html
Cerma Bryte works wonderfully. It's actually made to clean smooth top ceramic stove tops.
Easy Off No Fume Oven Cleaner. Works on enamel, porcelain, and fiberglass.
If nothing else has worked get some crystal Draino. It worked for me.