There are so many varieties of parasites, that no one has all of the answers. Killing parasites is a do it yourself project. You are unique as is your infestation.
In thinking about your original question, I wondered if you relied on chemical means only to kill the parasites? My experience was that a combo of mechanical and chemical means were necessary.
Changing the protocol periodically was also helpful. parasites adapt quickly and some things kill one type and not another. Have you been doing the same thing for 2 years?
Here are some things that I tried and felt made a difference:
Salt water flushes
Frozen cod liver oil capsules
Dosing with the moon
Enzymes between meals to attack the biofilm that parasites live in.
Betaine HCL at meals
Herbal formula composed of mostly Wormwood , Black-Walnut and cloves
Don't give up. Surrender is not an option.