Simplest and least harmful to the rabbit is to use oil and/or ointment.
Definitely ointment for the fur mites.
You need to use a non-toxic food grade oil, for example, olive oil, sunflower oil, etc. If you have vitamin E oil or vitamin E oil tablets and can cut one open and add it to the oil, it will be better. If you can get a dropper bottle, put some oil in it to make it easier to use. Warm the oil or ointment to room temperature so it doesn't get the rabbit upset or hurt it's ears with cold. Or, use Neosporin antibiotic ointment or the generic equivalent. You can get a generic at Dollar tree if you live where there is one.
Important: Don't attempt to clean ears of gunk until the oil has gone to work.
Drop a few drops into ears or spread ointment on until the brown gunk is coated. Let it stand about 30 minutes to penetrate. The rabbit will shake her head and flip her ears to remove the gunk, so put her in a place where she can do that without too much mess. This is one reason I use the ointment--cuts down on mess. Once the gunk has softened, you can gently remove it with cotton or a tissue. You don't have to get it all out, just enough to get the oil or ointment to properly contact the ear. Repeat the treatment every 2nd or third day to prevent any eggs from hatching for the next 3 weeks. The oil/ointment smothers the mites and keeps them from attaching to the rabbit. You can do the same for the fur mites, but bear in mind bunny may lick the area, so only safe products.
The mites are returning because:
1. You must continue the treatment to get mites that were missed and the eggs that continue to hatch.
2. The mites live in the environment as well as on the rabbit, so you have to sanitize cage or hutch/living area.
You can buy treatments made from oils and ointments with herbs in them online, but in a pinch, any edible oil will work. Small Pet Select sells a good gel for this, but I don't advise waiting for it to arrive.
Please start ASAP. Ear mites are dangerous parasites that can cause ear infections and kidney issues.