Is there any way to clean / dredge the filter of the so-called water auger that is deep in the ground or do you need to drill another well?

Connecting a really powerful and efficient pump should help. This will create a strong vacuum and loosen the filter by allowing a large flow of sludge around it, restoring the efficiency of the well. Just pump for at least 1 hour so that only gravel remains around the pipe. A very helpful indicator of when to stop pumping is observing the water coming out. If it flows clean and without sand, that will be the moment when pumping can be finished.