Have you tried cleaning with vinegar?
The only things you will need is a microwave safe bowl, wash cloth, rubber gloves, water, and vinegar .
How simple is that?
First you fill up the microwave safe bowl with 2/3 part water and 1/3 part vinegar.
You should use the biggest bowl that will fit in your microwave.
Then you just put a dish cloth in the bowl to soak up the water and vinegar.
Then you put it in the microwave and start the microwave on five to six minutes. This will boil the water.
The steam will start to loosen up everything on the walls of the microwave.
After the time is up, open up the microwave. Don't forget to put on gloves because it will be hot.
All you have to do then is rinse out the wash cloth of access water.
Use the wash cloth to wipe up debris on the walls and on the bottom of the microwave.
To rinse out the wash cloth of the access debris you can wring it out in the sink (if you have a garbage disposal), or shake the wash cloth in the trash.
And then rinse it out in the sink with tap water. Repeat this process until the microwave is clean.