While it is possible that a bout of scabies could survive the onslaught of all those treatments, it is extremely unlikely.
What is more likely is that you have been diagnosed incorrectly.
Scabies symptoms are not unique. They are similar to many other rashes, allergic reactions, bug bites, autoimmune conditions and so on. If you are not having any success with the treatments outlined on this site, it’s possible you have some other skin ailment. The only way you can be sure you have scabies is if a dermatologist or doctor has actually seen scabies mites or eggs on your skin.
There are various ways they can do this, but the two main ones are through microscopic glasses and/or skin scraping.
Microscopic glasses are things that look like huge snorkels/swimming goggles with microscopic lenses, which the doctor will put on and then examine your skin. What he is looking for are burrows, dead or live mites, and eggs. Normally if you have a well developed scabies infestation, it will not take him long to find these. My GP simply asked me which area was most itchy on my body, and for me that was my knee. He examined my knee with his microscopic glasses and it only took about 2-3 minutes before he confirmed he had seen a mite.
Skin scraping is when the doctor takes a glass slide, drops some dye or mineral oil on an affected area of the skin, and then scrapes several times to collect a sample. He/she should do this several times and collect several samples. This is then examined under a microscope to look for eggs, feces or mites.
If your doctor tries to tell you you have scabies but has not conducted either of these two tests, request them. Tell him/her you want a 100% confirmed diagnosis and you do not want to be applying toxic permethrin or ivermectin to your body without one.
INSIST on getting one or both of these tests done. It is impossible to give a certain diagnosis without it.
As with any profession, there are some dud doctors out there who will find this procedure cumbersome and just assume you have scabies or eczema or whatever else they can think of. All they are worried about is getting you out of their office and collecting their fee. If they refuse to do the necessary procedures to diagnose you properly, you are well within your rights to refuse to pay their fee and find another doctor. Remember, the doctor is there to serve you! Not the other way around. If you make a request, he/she is obliged to fulfill it. That’s what you are paying for.
Best of luck.