If the mold is truly black, you have more problems than just a case and mold. Black mold is toxic and needs to be taken care of IMMEDIATELY. My prior job was working as a contractor and I had to deal with black mold in several of the properties we purchased before renovating/remodeling. It can spread rampant and cause serious health risk, I can't stress enough the importance if it is actually black mold, that it needs to be taken care of, and NOW.
If it is toxic black mold, as you claim, it did NOT come from the case, but from your home. You may have a water leak in a hidden area of the house, as black mold takes about 2 weeks to colonize assuming it has warmth and moisture. If you attempt to disturb black mold by removing it without proper handling, there is a possibility the mold could release a large amount of spores and mycotoxins in the home which could cause serious sickness in your body which can vary from damage to your internal organs, hemorrhaging, respiratory problems, and more.
Take the focus off the case, and focus on the house you are living in.
Take a picture or so of what you are calling mold, let us see what you are talking about, because if it is from the CASE, I highly doubt it's mold, much less black mold.